Air-leak syndromes include Pulmonary interstitial emphysema Pneumomediastinum Pneumothorax Pneumopericardium Pneumoperitoneum or subcutaneous emphysema (rare) Pneumothorax and pneumomediastinum occur in 1 to 2% of normal neonates, probably because large negative intrathoracic forces created when the neonate starts breathing occasionally disrupt alveolar epithelium, which allows air to move from the alveoli into extra-alveolar soft tissues or spaces.