Resulting from weakened tracheal cartilages, this abnormality may be seen in association with a number of disorders including tracheobronchomegaly, COPD, diffuse tracheal inflammation such as relapsing polychondritis, as well as following trauma. On the radiographs, a reduction by almost 75% of the sagittal diameter at expiration is an excellent indicator of the diagnosis.
The increase in compliance is due to the loss of integrity of the wall's structural components and is particularly associated with damaged or destroyed cartilages. The coronal diameter of the trachea becomes significantly larger than the sagittal one, producing a lunate configuration to the trachea. The flaccidity of the trachea or bronchi is usually most apparent during coughing or forced expiration. In patients with COPD with high downstream resistance particularly high dynamic pressure gradients can be generated across the tracheal wall and it is likely that calibre changes of more than 50% can occur at expiration with normal tracheal compliance. As a result only a decrease in cross-section area of the tracheal lumen greater than 70% at expiration indicates tracheomalacia. Dynamic expiratory multislice CT may offer a meaningful alternative to bronchoscopy in patients with suspected tracheobronchomalacia10,11 because of its possibilities to provide morphological and functional information simultaneously. Dynamic expiratory CT may show complete collapse or collapse of greater than 75% of luminal cross-section (Fig. 1). Involvement of the central tracheobronchial tree may be diffuse or focal. The reduction of airway may result in an oval or crescent shape. The crescent shape is due to the bowing of posterior membranous trachea.
FIGURE 1 ■ Tracheobronchomalacia. Axial CT and sagittal reformation acquired during dynamic expiratory manoeuvre. Almost complete collapse of the trachea, (left) mainstem and (right) intermediate bronchi lumen. The airway lumen is crescent-shaped because of the anterior bowing of the posterior membranous trachea.
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