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Air trapping

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 compliance1.

Although not in common usage, the term “gas trapping” is more accurate.

It is a descriptor used in lung CT seem as a decreased attenuation of pulmonary parenchyma, especially manifest as less than normal increase in attenuation during expiration acquisition. Must be differentiated from the decreased attenuation of hypoperfusion secondary to locally increased pulmonary arterial resistance1.

The presence of air trapping can arise from a number of causes but usually suggests airway disease. 

Common conditions that lead to air trapping include

Other situations include

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