Air bronchogram

Air bronchogram refers to the phenomenon of air-filled bronchi (dark) being made visible by the opacification of surrounding alveoli (grey/white). It is almost always caused by a pathologic airspace/alveolar process, in which something other than air fills the alveoli. Air bronchograms will not be visible if the bronchi themselves are opacified (e.g. by fluid) and thus indicate patent proximal airways.

Air bronchograms can be seen with several processes:

• pulmonary consolidation
• pulmonary oedema: especially with alveolar oedema ³
• non-obstructive atelectasis
• severe interstitial lung disease
• neoplasms: bronchioloalveolar carcinoma; pulmonary lymphoma
• pulmonary infarct
• pulmonary haemorrhage
• normal expiration

Air bronchograms that persist for weeks despite appropriate antimicrobial therapy should raise the suspicion of a neoplastic process. CT may be planned in such cases.

Radiographic features

Ultrasound

Sonographic air bronchograms arise as a secondary consequence of an extreme perturbation of the air-fluid relationship in lung parenchyma, in which fluid-filled alveoli act as an excellent acoustic medium and allow visualisation of the lung parenchyma. Arborising tubular structures representing the bronchial tree may be visualised which, when patent, appear to contain punctiform-to-linear foci. These structures may remain fixed in position throughout the respiratory cycle or be observed to propagate distally and proximally with inspriation and expiration, respectively. This distinction is important for determining the aetiology of the underlying pathology ⁴;

• dynamic air bronchograms move centrifugally with respiration
  • represent fluid mixed with air inside larger bronchi, which are in continuity with the gas inspired by the patient
  • indicates a non-retractile consolidation, ruling out resorption atelectasis
  • specificity of 94% and a positive predictive value of 97% for pneumonia as the cause of the consolidation
• static air bronchograms lack detectable movement 
  • indicate isolated, trapped air, consistent with resorptive atelectasis

See also

• airspace disease