Pulmonary lymphatic air: locating "pulmonary interstitial emphysema" of the premature infant.

Pulmonary interstitial air in the premature infant, a complication of hyaline membrane disease and respiratory supportive treatment, is usually described as representing freely dissecting air that has escaped from terminal air spaces to dissect along the bronchovascular bundles of the lung. By inflating the lung and fixing it in this state, the interstitial air is identified within the lymphatics of the interlobular septae and visceral pleura. On a radiography, this lymphatic air is seen as a pattern of fine linear lucencies involving a lobe or an entire lung. With increasing distension, oval and cystic lucencies are seen representing air in dilated septal lymphatics and lymphatics of the visceral pleura. Pneumothorax results from rupture of these collections into the pleural space.