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.
Although not in common usage, the term gas trapping is more accurate.
Air trapping is a descriptor used in lung CT seem 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.
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:
- 1. Austin JH, Müller NL, Friedman PJ et-al. Glossary of terms for CT of the lungs: recommendations of the Nomenclature Committee of the Fleischner Society. Radiology. 1996;200 (2): 327-31. Radiology (citation) - Pubmed citation
- 2. Webb WR, Műller NL, Naidich DP. High-resolution CT of the lung. Lippincott Williams & Wilkins. (2008) ISBN:0781769094. Read it at Google Books - Find it at Amazon
- 3. Tanaka N, Matsumoto T, Miura G et-al. Air trapping at CT: high prevalence in asymptomatic subjects with normal pulmonary function. Radiology. 2003;227 (3): 776-85. doi:10.1148/radiol.2273020352 - Pubmed citation
- 4. Arakawa H, Webb WR. Air trapping on expiratory high-resolution CT scans in the absence of inspiratory scan abnormalities: correlation with pulmonary function tests and differential diagnosis. AJR Am J Roentgenol. 1998;170 (5): 1349-53. Pubmed citation
- 5. Tsiligiannis T, Grivas T. Pulmonary function in children with idiopathic scoliosis. Scoliosis. 2012;7 (1): 7. doi:10.1186/1748-7161-7-7 - Free text at pubmed - Pubmed citation
- 6. Miller WT, Chatzkel J, Hewitt MG. Expiratory air trapping on thoracic computed tomography. A diagnostic subclassification. Ann Am Thorac Soc. 2014;11 (6): 874-81. doi:10.1513/AnnalsATS.201311-390OC - Pubmed citation