Imaging in Pulmonary Interstitial Emphysema
- Author: Beverly P Wood, MD, MSEd, PhD; Chief Editor: John Karani, MBBS, FRCR more...
Overview
Pulmonary interstitial emphysema (PIE) is an iatrogenic pulmonary condition of the premature infant with immature lungs. PIE occurs almost exclusively in association with mechanical ventilation. The ventilatory pressure 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. The development of PIE is demonstrated in the images below.[1, 2]
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. Preferred examination
PIE may be identified with a frontal chest radiograph. Disease progression is assessed with sequential studies.[3]
Limitations of techniques
In an ill infant, it may be difficult to differentiate PIE from lucent overdistension 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.
Radiography
On radiography, PIE appears as linear, oval, and occasional spherical cystic air-containing spaces throughout the lung parenchyma. The interstitial changes are initially linear but may become more cystic as the air in the interstitium congregates locally. Subpleural cysts also develop and may rupture, producing a pneumothorax. The heart tends to get smaller as intrathoracic pressure increases; this results in diminished venous return into the chest. Overall lung volume is increased; however, the lungs are less compliant because they are splinted at a large volume by the air within the interstitium. Gas exchange is reduced by the increase in distance between the pulmonary vascular bed and the airspaces.
The images below demonstrate the radiographic characteristics of PIE.
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. 
Pulmonary interstitial emphysema developing in an infant with respiratory distress syndrome at age 1 day. 
By age 2 days, the infant has not improved, and pulmonary interstitial emphysema is more extensive. 
Close-up examination shows the typical linear pattern of pulmonary interstitial emphysema. 
Shortly before death, despite efforts to decrease ventilatory pressures, the lungs remain hyper-aerated with diffuse pulmonary interstitial emphysema. 
Air in the lymphatics may rupture, causing pneumothorax, and can dissect into the peritoneum through potential openings in the diaphragm. This infant has pulmonary interstitial emphysema, pneumothoraces, and pneumoperitoneum. Degree of confidence
Linear gas collections in the periphery of the lung, in association with an increased demand for respiratory support, are diagnostic of PIE. Increasing lung volumes also strongly support a diagnosis of PIE.
False positives/negatives
Early BPD may present as focal areas of hyperaeration secondary to partial bronchial obstruction. The pattern closely resembles PIE, although the lucency is less linear in BPD. At histopathology, many lungs of infants with BPD demonstrate PIE that was not seen radiographically.
Cochran DP, Pilling DW, Shaw NJ. The relationship of pulmonary interstitial emphysema to subsequent type of chronic lung disease. Br J Radiol. Dec 1994;67(804):1155-7. [Medline].
[Best Evidence] Greenough A, Dimitriou G, Prendergast M, Milner AD. Synchronized mechanical ventilation for respiratory support in newborn infants. Cochrane Database Syst Rev. Jan 23 2008;CD000456. [Medline].
Jabra AA, Fishman EK, Shehata BM. Localized persistent pulmonary interstitial emphysema: CT findings with radiographic-pathologic correlation. AJR Am J Roentgenol. Nov 1997;169(5):1381-4. [Medline].
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