Retrocardiac pneumomediastinum: radiographic finding and clinical implications.

Fourteen neonates with posterior mediastinal air collections (retrocardiac pneumomediastinum) are described. In the majority of the infants (13 of 14), the mediastinal air developed as a complication of assisted ventilation. It is suggested that the retrocardiac pneumomediastinum represents air trapped in a potential space in the mediastinum posterior to the heart and not within the pulmonary ligament. The collections have a variable shape and size and rarely may produce a tension phenomenon elevating the posterior, inferior portion of the heart off of the diaphragm. There was a strong association of retrocardiac pneumomediastinum with other manifestations of extraalveolar air, including pulmonary interstitial emphysema (13 of 14 infants), pneumothorax (10 of 14 infants), dissection of air into the soft tissues of the neck (10 of 14 infants), and pneumoperitoneum (5 of 14 infants).