Gravity-dependent atelectasis

Last revised by Henry Knipe on 22 Nov 2022

Gravity-dependent atelectasis refers to a form of lung atelectasis that occurs in the dependent portions of the lungs.

Gravity-dependent atelectasis occurs due to a combination of reduced alveolar volume and increased perfusion. Due to gravity, it usually has a dependent 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.

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