Pulmonary interstitial emphysema (PIE) is an iatrogenic pulmonary condition of the premature infant with immature lungs. PIE occurs almost exclusively in association with respiratory distress syndrome and mechanical ventilation.
Independent risk factors for mechanical ventilation-caused pulmonary interstitial emphysema are higher oxygen during resuscitation and a higher need for surfactant and ventilatory pressures before diagnosis.
The ventilatory pressure that is used to keep the alveolar ducts open also may cause the alveolar duct to rupture (usually at the junction of the bronchiole and alveolar duct); this in turn leads to the escape of air into the pulmonary interstitium, lymphatics, and venous circulation.
PIE may be identified with a frontal chest radiograph. Disease progression is assessed with sequential studies.
In an ill infant, it may be difficult to differentiate PIE from lucent overdistention of the bronchioles, although overdistended distal airways tend to be round and of uniform diameter, whereas PIE tends to be ovoid in the direction of the bronchovascular bundles. In addition, the lesions of PIE tend to be of different sizes. It is also difficult to differentiate PIE from early bronchopulmonary dysplasia (BPD) with uneven patterns of aeration. Computed tomography (CT) scanning of the chest can be a helpful diagnostic tool if doubt about the diagnosis remains. The presence of subpleural PIE, in which there is an interstitial air collection in the subpleural region of the lungs excluding the bronchovascular bundle, on CT scan suggests single or multiple alveolar rupture(s) as an origin of pneumomediastinal air.
A study by Donnelly et al found that 82% of patients with persistent pulmonary interstitial emphysema (14 of 17 patients) had characteristic CT findings (central lines and dots surrounded by radiolucency).
The development of PIE is demonstrated in the images below.
Anteroposterior examination of the chest at age 1 hour in this 27-week premature infant shows severe diffuse respiratory distress syndrome.
At 7 hours, the lungs are overexpanded with multiple linear areas of lucency, indicating pulmonary interstitial emphysema.