Pathologic accumulation of air in the interstitium of the lungs, which is caused by the rupture of alveoli and terminal bronchioles, and is most often seen in premature infants that need mechanical ventilation for respiratory distress syndrome. The disease is interstitial emphysema (MONDO_0000923). Also known as: PIE, interstitial emphysema of lung, pie, pulmonary interstitial emphysema.