Gravity-dependent atelectasis

Gravity-dependent atelectasis refers to a form of lung atelectasis which occurs in the dependent portions of the lungs due to a combination of reduced alveolar volume and increased perfusion. Being 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 . These gradients increase in the presence of lung disease that increases the weight of the lung causing atelectasis.

Pathology

Etiology

• bedridden patients
• patients with prolonged shallow breathing
• impaired mucociliary clearance
• pneumonia
• pulmonary edema

Differential diagnosis

• early interstitial lung disease: prone CT chest can usually differentiate