Air trapping
Updates to Article Attributes
Air trapping in chest imaging refers to retention of excess gas (“air”) in all or part of the lung, especially during expiration, either as a result of complete or partial airway obstruction or as a result of local abnormalities in pulmonary compliance. It may also sometimes be observed in normal individuals 3.
Terminology
Although not in common usage, the term gas trapping is more accurate.
Radiographic features
Air trapping is a descriptor used in lung CT seen as a decreased attenuation of pulmonary parenchyma, especially manifested as a less than normal increase in attenuation during expiratory acquisition. This appearance must be differentiated from the decreased attenuation of hypoperfusion secondary to locally increased pulmonary arterial resistance 1.
Differential diagnosis
The presence of air trapping can arise from a number of causes but usually suggests airway disease (often small airways disease). Air trapping can occur in isolation, or in association with bronchiectasis, interstitial lung disease, or rarely tree-in-bud opacity, which can help narrow the aetiology 3,6:
- in isolation
- with bronchiectasis
- with interstitial lung disease
Other uncommon conditions include 5,6:
-
pulmonary tumourlets:
- neuroendocrine cell proliferation spectrum
- diffuse idiopathic pulmonary neuroendocrine cell hyperplasia (DIPNECH) 7
- scoliosis: especially when severe
- vasculitis
Causes of air trapping on high-resolution CT chest (mnemonic)
-<li><a title="Asthma" href="/articles/asthma-1">asthma</a></li>- +<li><a href="/articles/asthma-1">asthma</a></li>
-<li><a href="/articles/vasculitis">vasculitis</a></li>-</ul>- +<li><a title="Vasculitis" href="/articles/vasculitis">vasculitis</a></li>
- +</ul><p>Causes of air trapping on high-resolution CT chest (<a title="mnemonic" href="/articles/causes-of-air-trapping-on-high-resolution-ct-chest-mnemonic">mnemonic</a>)</p>
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