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Airway (Bronchial) Patterns

89

Forms

Complete airway obstruction: Opacity and decreased volume

Partial obstruction: Lucency and increased volume

Wall thickening: Tram tracks, central cystic spaces or circles

For the differential diagnosis, look for the following.

Opacities: Endobronchial malignancies; granulomas; inflammatory, benign or congenital masses; mucous plugs; foreign bodies potentially causing complete obstruction

Lucencies: Chronic obstructive pulmonary disease (COPD), cysts, blebs, pneumatoceles

Thickening: Bronchiectasis, chronic bronchitis

Complete Obstruction

Obstruction of a bronchus or airway results in complete obstruction.

Radiological Signs

Direct Signs: Displacement of interlobar fissures

Indirect Signs: Opacification, mediastinal shift (ipsilateral), hilar displacement, elevation of hemidiaphragm, crowded vasculature, compensatory hyperinflation of unaffected lung, “shifting” granuloma sign and juxtaphrenic peak

The four main types of mechanisms of obstruction and resultant atelectasis are as

follows:

1.Resorptive/Obstructive: This type is caused by a complete bronchial obstruction. If there is no flow, then air becomes absorbed from the lung. Oxygen gets absorbed much more rapidly than ambient air. (E.g., a ventilator patient on 100% oxygen will collapse within minutes to hours.)

2.Passive/Compressive: This type is caused by extrinsic pressure from air, fluid, or mass (tumors, bullae, or abscesses). A large pleural fluid collection or pneumothorax could produce virtual complete collapse of the lobe.

3.Cicatricial: Areas of pulmonary fibrosis can cause reduced alveolar volume. It can be focal or diffuse. When focal, it is generally associated with old granulomatous infection, typically TB. However, it may be diffuse, as seen typically in idiopathic pulmonary fibrosis.

4.Adhesive: This type occurs in association with surfactant deficiency and subsequent microatelectasis. Type II pneumocytes can be injured from inhaled anesthetic agents, ischemia, or radiation, therefore, causes include general anesthesia, adult respiratory distress syndrome, hyaline membrane disease, and acute radiation pneumonits.