Atelectasis: resorption, compression and contraction
- Lesion
Atelectasis is collapsed or never-expanded lung. Air is absorbed behind a blocked airway, pushed out by pleural fluid or air, or held in by scar.
What it is
Atelectasis means lung that is not filled with air. In adults it comes in three acquired forms, defined by how the alveoli lose their air. The type is told by the mediastinum: it moves toward a lung that has lost volume and away from a lung pressed by the pleural space. Except when scar causes it, atelectasis can reverse.
Structure
- Gross: the collapsed area is dark red-purple, airless, sunken below the pleura and firm or rubbery.
- Microscopy: alveolar walls lie close together with slit-like spaces; capillaries remain perfused.
- In long-standing collapse the walls fibrose and infection can complicate the airless lung.
Step by step
- The cause removes air from the alveoli: absorption behind an obstruction, external pressure, or scar that will not stretch.
- Collapsed alveoli are still perfused, so blood crosses the lung without taking up oxygen (a shunt).
- Hypoxaemia follows, roughly in proportion to how much lung has collapsed.
- Secretions stagnate in the airless segment and bacteria multiply: pneumonia.
- If the cause is removed early (plug cleared, effusion drained) the lung re-expands.
The three acquired types
| Type | Mechanism | Mediastinum | Examples |
|---|---|---|---|
| Resorption | Air absorbed behind a blocked airway | Shifts toward the collapse | Mucus plug, foreign body, endobronchial tumour |
| Compression | Pressure from the pleural space | Shifts away from the collapse | Effusion, haemothorax, pneumothorax |
| Contraction | Fibrosis prevents expansion | Toward the scarred side | Pulmonary or pleural fibrosis |
Clinical notes
- After abdominal or chest surgery: shallow breathing and mucus plugs; early mobilisation and deep breathing prevent it.
- A central tumour that blocks a bronchus may first show as lobar collapse on the chest film.
- Tension pneumothorax and large effusions cause compression atelectasis with mediastinal shift to the other side.
Test yourself
Think of the answer, then tap the question to see it.
Toward which side does the mediastinum move in resorption atelectasis?
Toward the collapsed lung, because that lung has lost volume after the air behind the obstruction was absorbed.
Which type of atelectasis is usually irreversible?
Contraction atelectasis, caused by lung or pleural fibrosis.
Why does atelectasis lower the blood oxygen?
The collapsed alveoli are still perfused but not ventilated, so blood passes through as a shunt without picking up oxygen.
Elsewhere in DurgiPedia
Connections
Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Collapsed Lung (MedlinePlus, US National Library of Medicine, 2025).
Spotted a mistake?We are always improving for the community. Tell us what is wrong and our team will review it.Report a mistake
Representative model, for educational purposes only.