Introduction
This topic covers how X-ray examinations, mainly the plain chest radiograph with CT as the key complement, help recognise and classify diseases of the trachea, the main bronchi and the smaller airways. Airway disease often shows only indirect signs on plain film, so the student must know both the direct and the indirect radiographic findings and which investigation to request next.
Principles of airway imaging
The plain chest radiograph (PA and lateral) is the first examination. Normal airways are visible only as air-filled lumens, so the trachea should be central and the bronchi are seen mainly through the lung fields. Abnormal airways are recognised by changes in lung density, volume, and the position of the mediastinum. Expiratory or lateral views are used when air trapping or tracheal collapse is suspected, and high-resolution CT (HRCT) gives direct assessment of bronchial walls, lumen and calibre.
- Hyperlucency: increased blackness of a lung or lobe, with reduced vascular markings.
- Air trapping: the affected lung does not deflate on expiration.
- Atelectasis or collapse: volume loss with crowding of vessels, displacement of fissures and shift of the mediastinum towards the affected side.
- Mediastinal shift: towards the lesion in collapse, away from it in hyperinflation.
- Bronchial wall thickening and visible dilated bronchi, seen as parallel lines or ring-like shadows.