Imaging description

A premature newborn infant with respiratory distress was intubated at birth. A frontal chest radiograph (Fig. 20.1a) was obtained which demonstrated an endotracheal tube and nasogastric tube in place. The lungs were mildly underinflated with diffuse symmetric bilateral hazy (ground glass) opacity of the lungs. The appearance was thought to be most consistent with surfactant deficiency although at this early stage there could be some contributory element of residual fetal lung fluid. While neonatal pneumonia, especially infection with group B Streptococcus, could have this appearance, there was no clinical history or other findings to suggest infection. There was an unusual central air collection extending from just above the heart to the diaphragm and posterior in location on the lateral view most suggestive of a posterior retrocardiac pneumomediastinum. There was no history of a traumatic tube placement and the air collection dissipated without any specific treatment.

Importance

Retrocardiac pneumomediastinum has been variously thought to be loculated air in the infra-azygos space or air in the pulmonary ligament. In general, pulmonary ligament air tends to adopt a slightly more parasagittal location consistent with the anatomic location of the pulmonary ligament, whereas air in the infra-azygos mediastinum is more midline in position, as in this case. Extension of air from this space superiorly is usually prevented by fascia reflected from the underside of the carina to the fibrous layer of the parietal pericardium. However, the air collection in this case does seem to be present more superiorly than an infra-azygos location.