Pulmonary interstitial emphysema (PIE) is a form of air block most frequently seen in ventilated preterm infants with severe lung disease; it is rarely reported in spontaneously breathing term infants.
References
Spontaneous pulmonary interstitial emphysema in a term unventilated infant. Freysdottir D, Olutoye O, Langston C, Fernandes CJ, Tatevian N. Pediatr Pulmonol. 2006 Apr;41(4):374-8. PMID: 16447182