Air bronchograms appear on a CXR when something other than air is present in the alveoli adjacent to a bronchus or bronchiole, making the air-filled bronchus more conspicuous than normal. That something is usually fluid, and this is most commonly due to pneumonia although pulmonary oedema and haemorrhage can also cause air bronchograms. The presence of an air bronchogram indicates that the airway proximal to it is patent, which can be a helpful sign. In the magnified example here, the air bronchograms were caused by extensive pneumonia in this patient’s lingula and left lower lobe. The image on the right has been manipulated to further increase the conspicuity of the air bronchograms for illustrative purposes. Note the left internal jugular venous line.