Infraazygous pneumomediastinum in the newborn.

Six neonates receiving assisted ventilation developed loculated posterior mediastinal gas collections. Relation to other mediastinal structures localizes these gas collections to the infraazygous region, and the midline location distinguishes infraazygous pneumomediastinum from air within the pulmonary ligaments. Infraazygous pneumomediastinum does not communicate freely with the anterior mediastinum, but often dissects cephalad and is frequently associated with pneumoperitoneum.