Air Bronchogram

You may come across the term “air bronchogram” when reading a radiology report concerning the chest.  This finding may be seen on chest X-rays and CT scans. This article will discuss what an air bronchogram means can and what this finding can represent.

What Is an Air Bronchogram?

An air bronchogram refers to the appearance of air-filled bronchi (the tubes that carry air to the lungs) that become visible on an imaging scan within an area of airless or opacified abnormal lung. When lung tissue becomes dense from infection, inflammation, or fluid accumulation, the bronchi stand out against this background, creating the air bronchogram sign.  The air bronchogram sign implies that the more proximal bronchi are open and not blocked by something like a tumor.

Imaging Findings: How Air Bronchograms Appear on Scans

• Chest X-ray: Air bronchograms appear as dark, branching structures within an area of whiteness (opacity) in the lung. This is a key sign of alveolar (air sac) filling due to infection, fluid, or other causes.
• CT Scan: On CT imaging, air bronchograms are better seen, showing fine branching airways within a consolidated or opacified lung region. CT scans can also help determine the cause of the consolidation, such as pneumonia, pulmonary edema, or lung cancer.

Causes of Air Bronchograms on Imaging

Multiple lung conditions can lead to the appearance of air bronchograms. These include:

1. Pneumonia – Bacterial, viral, or fungal infections can cause lung tissue to become inflamed and filled with pus or fluid, making air bronchograms a classic sign.
2. Pulmonary Edema – Fluid accumulation in the lungs due to heart failure or other conditions may produce this imaging feature.
3. Lung Cancer – Some tumors causing lung consolidation can demonstrate air bronchograms.
4. Atelectasis (Lung Collapse) – Partial lung collapse can sometimes result in air bronchograms, depending on the underlying cause.
5. Pulmonary Hemorrhage – Bleeding into the lung tissue from trauma, blood disorders, or inflammatory conditions may present with this finding.
6. Acute Respiratory Distress Syndrome (ARDS) – Severe lung injury causing widespread inflammation and fluid buildup often shows air bronchograms on imaging.

What does it mean when the lung is opacified but there are no air bronchograms?

Conditions to consider include:

• Pleural Effusion: Unlike consolidation, pleural effusion involves fluid outside the lung, often causing lung compression without visible air bronchograms.
• Interstitial Lung Disease: This condition affects the lung tissue between air sacs, usually appearing without air bronchograms.
• Masses or Nodules: Tumors may block bronchi and present without the air bronchogram sign unless causing secondary consolidation.

How Radiologists Interpret Air Bronchograms

Radiologists assess air bronchograms in the context of a patient’s symptoms, medical history, and other imaging features. The presence of air bronchograms suggests that the bronchi proximal to the opacified lung are open and not blocked. This can be used to narrow the diagnostic possibilities.

Personal Insight: In my practice, air bronchograms are most frequently associated with pneumonia. When I see this sign on a chest X-ray, I often correlate it with clinical symptoms like fever, cough, and shortness of breath to confirm the diagnosis. In cases of heart failure, I carefully evaluate for accompanying pulmonary edema, which also produce air bronchograms but requires different management.  Consolidation with air bronchograms which does not go away with treatment or persists over weeks becomes more concerning for cancer.

When Should You Be Concerned?

The presence of opacified lung and air bronchograms does not indicate a specific diagnosis on its own.  But the findings should prompt further medical evaluation. If found on an imaging report, your doctor may recommend additional tests, such as blood work, sputum analysis, or follow-up imaging, depending on your symptoms and risk factors.

Conclusion

Air bronchograms are an important imaging finding that indicates open airways within consolidation due to infection, fluid accumulation, or other underlying conditions. By understanding this radiology term, patients can have more informed discussions with their doctor regarding lung findings on imaging tests.  If you see “air bronchogram” on your radiology report, it is important to dicuss the findings with your doctor for appropriate next steps.

References:

1. Radiopaedia: Air Bronchogram – https://radiopaedia.org/articles/air-bronchogram
2. American Lung Association: Pneumonia – https://www.lung.org/lung-health-diseases/lung-disease-lookup/pneumonia
3. https://www.sciencedirect.com/science/article/abs/pii/S0720048X23005089