**4.4.2 Overinflation of all three lobes of the right lung**

Rarely produced by anomalous location of the left pulmonary artery impinging on the right main stem bronchus or occassionally with absent pulmonary valve type of tetralogy of Fallot and secondary aneurysmal dilatation of the pulmonary artery. Some neonates have lobar overinflation while on assisted ventilation, suggesting an acquired cause.

#### **4.4.3 Broncho-pulmonary dysplasia**

A form of chronic lung disease that develops in preterm neonates treated with oxygen and positive-pressure ventilation. Injury to small airways and pulmonary vasculature can interfere with alveolarization (alveolar septation), leading to alveolar simplification and reduction in the overall surface area for gas exchange. Premature birth and subsequent events (eg, exposure to oxygen, mechanical ventilation, inflammatory agents, infection) shifts the lung development towards premature maturation with an arrest in development and a loss of future gas exchange area.
