This photo is from a premature neonate who required controlled ventilation. The lungs of such a patient would probably show pulmonary interstitial emphysema.

Pneumopericardium can develop from trauma, a fistula from an air-containing structure such as the esophagus, or the presence of gas-producing infectious organisms in the pericardium. Trauma can be either blunt external trauma or barotrauma. High-pressure ventilation in premature neonates is especially likely to lead to this complication. In these infants the air, under pressure, initially dissects into the interstitial spaces of the lungs and then, in some cases can produce pneumothorax, pneumomediastinum, and/or pneumopericardium. Small amounts of air are tolerated if the accumulation is slow but rapid accumulations have adverse hemodynamic consequences.