Air bronchograms: What are they? Pathologies, Mechanism and General Characteristics

They are findings that can be observed on a chest radiograph, however, they can be observed in another type of study such as a chest CT scan.

In these images you can visualize the air present in the patient’s bronchi.

The air bronchograms are a sign of the existence of a pathology in the air space that exists within the lung when observed as nebulous opacities.

The air brocogram can be defined as the existence of fluid or soft tissue in the area of ​​the bronchus that should normally be full of air and that allows it to be more visible.

There are many different things that could fill this space and produce the image of an air bronchogram, such as: fluid, blood, exudate and others.

Pathologies of air bronchograms

Air bronchograms can be observed in several processes:

Lung consolidation: this is an inflammation of the alveoli , caused by infection caused by bacterial microorganisms such as Streptococcus pneumoniae (pneumococcus) or Klebsiella.
Pulmonary edema, especially with alveolar edema: this inflammation is caused by an accumulation of fluid in the spaces located between the blood capillaries and the alveolus, usually caused by heart failure.
Non-obstructive atelectasis: inflammation is caused by pleural effusion, presence of intrapulmonary fluid, caused by tumors, lung scars, surfactant deficiency or traumas.
Severe interstitial lung disease:is an inflammation produced by the accumulation of dust in the alveoli with other air particles such as toxic gases, iron, asbestos and silica.
Neoplasms: bronchioloalveolar carcinoma, pulmonary lymphoma, caused by epithelial cells in multiple diffuse nodules that are found in the peripheral cells of the bronchioalveolar region .
Pulmonary infarction: it is due to the presence of clots that have migrated from another part of the body to an artery of the lungs.
Pulmonary hemorrhage: is caused by damage to the pulmonary vessels that fills the alveoli with blood.

Mechanism

The airways under normal conditions can not be observed on a chest radiograph, since the structures present in the lung are filled with air.

These lung fields are seen on radiolucent radiographs and the bronchi can not be visualized separately.

When the aerated lungs become opaque, due to the presence of inflammatory exudates, liquids or particles.

The bronchi can be observed since they stand out as radioluscentes in contrast with the adjacent alveoli that appear radiopaque.

These are called air bronchograms and are diagnostic of consolidation; the visualization of the air bronchogram helps in the identification of underlying pathological cases.

General characteristics of air bronchograms

More specific tests should be performed on air bronchograms that last for several weeks despite the application of appropriate antimicrobial therapy. Like the computed tomography, since this can be a neoplastic process.

The morphology of an air bronchogram can provide some important features to perform the differential diagnosis between pneumonias and atelectasis .

The radiological signs that could be observed in pulmonary hyperinflation such as interstitial fibrosis, cancer, asthma, do not cause air bronchogram.

When the intrapulmonary blood vessels contain blood, they can be seen on radiological images and on a CT scan.

Since the density of the blood is greater than those of the pulmonary parenchyma that surround it.

In a computed tomography, the air bronchogram sign is clearly visible, because it has a greater power of density discrimination.

Interstitial disease or peripheral patchy lung infiltrates do not usually produce sufficient opacity to cause air bronchogram.

The air bronchogram represents a sign of pulmonary radiology in which the bronchi usually have thin walls and are almost invisible.

These are transformed into tubular branching structures that can be made visible by the content of a substance other than air.

The substance that can replace air can be water, fluids, blood, pus or, with little chance, tumors.

The alveoli will be occupied by different substances depending on the pathology they present:

  • In acute respiratory distress syndrome: the alveoli fill with fluid.
  • In alveolar pulmonary edema: the air space is filled with fluid.
  • In pulmonary hemorrhage: airspace is filled with blood
  • In the aspiration: the air space is filled with gastric juices.
  • In pneumonia: the air space is filled with the inflammatory exudate of bacteria.
  • Interstitial lung disease:  The air space is filled with solid particles.
  • Drowning: the air space is filled with water.