Blunt traumatic rupture of a mainstem bronchus: spiral CT demonstration of the "fallen lung" sign.

Tracheo-bronchial injuries occur in less than 1 % of blunt chest trauma patients. Indirect signs, such as pneumomediastinum, pneumothorax, and/or subcutaneous emphysema, are revealed on admission plain films and chest CT survey. In most instances, however, tracheobronchoscopy is mandatory in assessing the definite diagnosis of tracheo-bronchial lesion. Occasionally, an abnormal course of a mainstem bronchus or a "fallen lung" sign, featuring a collapsed lung in a dependent position, hanging on the hilum only by its vascular attachments, may allow for CT diagnosis of a blunt traumatic bronchial injury.