What is the significance of air bronchogram?

The presence of an air bronchogram is of great clinical importance as it suggests that there is an airspace disease with a collapse or near-collapse of the corresponding alveoli.

Bronchi are usually not visible on frontal chest X-rays since the air density within them is similar to that of the surrounding lung parenchyma. Their visualization becomes possible when they are surrounded by areas of increased density, such as pneumonia or tumor, or when the alveolar parenchyma is rarefied, as in emphysema.

The radiographic appearance of air bronchograms mimics the appearance of blood vessels. Thus, it is important for the clinicians to differentiate between them, based on the shape and course of the branching shadows and the presence of pulmonary vessels at the hilum.