Pulmonary Interstitial Emphysema

Pulmonary interstitial emphysema (PIE) is a condition in which air leaks into the peribronchovascular (ie, interstitial) space and compresses adjacent structures.

PIE occurs when air leaks into the peribronchovascular space due to the rupture of overdistended alveoli.  Air accumulates in the perivascular space and compresses adjacent bronchioles and vessels, resulting in:

• increased airway resistance, which can lead to air trapping and impaired gas exchange.
• decreased pulmonary venous return, which can lead to impaired cardiac output.

In addition, trapped air in the perivascular space leads to decreased pulmonary compliance, further impairing gas exchange.

PIE is a type of pulmonary air leak disorder.  Air that leaks into the perivascular space can dissect along the perivascular connective tissue sheath, and the resultant disorder depends on the location of accumulated air.  Other types of pulmonary leak disorders include pneumothorax (ie, air in pleural space), pneumomediastinum (ie, air in mediastinum), and pneumopericardium (ie, air in pericardial space).  Less commonly, air can dissect into the peritoneal space (ie, pneumoperitoneum) or subcutaneous tissue (ie, subcutaneous emphysema).