Gravity dependant atelectasis refers to a form of lung atelectasis which occurs in the dependant portions of the lungs due to a combination of reduced alveolar volume and increased perfusion. Being due to gravity, it usually has a dependant and subpleural distribution. It is very commonly seen in the posterior lung bases on CT, particularly in elderly individuals.
In normal lung, gravity gradients exist in end-inspiration between the apex and lung base of 4:1 in the erect patient and between the anterior and posterior lung of 2.5:1 in the supine patient 1. These gradients increase in the presence of lung disease that increases the weight of the lung causing atelectasis.
- 1. Woodring JH, Reed JC. Types and mechanisms of pulmonary atelectasis. (1996) Journal of thoracic imaging. 11 (2): 92-108. Pubmed
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