Cervical trachea: dynamics in response to herniation of the normal thymus.

Nineteen infants aged 2 months to 2.5 years, first seen predominantly with stridor, were noted to have intermittent soft-tissue mass effect in the upper airway during routine evaluation with fluoroscopic or radiographic methods. The cervicothoracic trachea was always buckled posteriorly and, in almost all instances, to the right during forced exhalation (crying). Real-time ultrasound examination with the neck extended was used in these patients to define the cause of the tracheal dynamics. The intermittent cephalic movement of the homogeneous echotextured thymus from the anterior mediastinum into the neck was determined to be the probable cause of the mass effect in these infants. Magnetic resonance imaging in three infants confirmed this finding. The intermittent, physiologic suprasternal movement of the thymus in these infants did not by itself cause any luminal compromise of the trachea and did not result in any respiratory difficulty in these infants.