Tracheomalacia..part 1..Causes and Diagnosis...

In adults, the most common cause of tracheomalacia is prolonged mechanical ventilation; high pressures in the endotracheal tube cuff may cause localized ischemic injury to the tracheal wall (the cartilage and the membranous sheath).

Other causes of segmental tracheomalacia include prolonged external pressure on the tracheal wall, such as may be caused by a large substernal goiter or a congenital vascular sling (e.g., a right-sided aortic arch with an aberrant subclavian artery).

More diffuse tracheomalacia is encountered in patients with the rare conditions of tracheobronchomegaly (Mounier-Kuhn syndrome) and relapsing polychondritis.

The diagnosis of tracheomalacia may be made with the use of fiberoptic bronchoscopy, but the speed of image collection on modern multidetector CT equipment makes chest CT a useful alternative means of diagnosis.
Images should be obtained during inspiration and expiration and then compared. For images collected during expiration, the goal is to maximize the abnormal movement of the posterior tracheal wall (or any other malacic portion of the wall).

The best time to obtain the image is near but not at the end of exhalation, when the pleural pressure is still positive.

Precise criteria for radiographic diagnosis of tracheomalacia have not yet been defined, but many radiologists use a luminal narrowing of 50% on exhalation as a benchmark.

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