Pulmonary interstitial emphysema

Pulmonary interstitial emphysema (PIE) refers to pathological lung changes that follow rupture of overdisteneded alveoli. It typically results following barotrauma in infants who have respiratory distress syndrome. 

Pathophysiology

Following alveolar rupture due to their poor compliance, air tracts through the interstitum and may even migrate peripherally (pneumothorax) or centrally (pneumomediastinum). It nearly always occurs during 1st week of life and in newborns on ventilatory support. It is typically a transient phenonenon but occasionally can be chronic (persistent).

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.

Radiographic features

Plain film : Chest radiograph

• radiograph shows bubbles (round) or streaky (linear) radioculencies in the interstitum radiating from the hilum, usually involving a single lobe.
• affected segment is often hyperexpanded
• patients may have pneumothorax, pneumomediastinum, or pneumopericardium.
• in supine patients, pneumomediastinum is evident by the sharp mediastinum sign
• heart tends to get smaller as intrathoracic pressure increases and results in diminished venous return into the chest.

CT

• not usually part of routine investigation (unnecessary risk of radiation exposure)
• shows cystic radiolucencies in affected segment.
• may characteristically show a line and dot pattern with surrounding radiolucency ⁴.
• allows better visualisation of a pneumothorax or pneumomediastinum 

• partially treated hyaline membrane disease (surfactant deficiency)
• bronchopulmonary dysplasia
• congenital cystic adenomatoid malformation (CCAM)
• congenital lobar emphysema
• congenital diaphragmatic hernia