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Pulmonary hypoplasia is common in the perinatal period and a significant cause of death in newborn infants. Wigglesworth and Desai reported an incidence of 14.5% in a series of perinatal necropsies.1 Renal or urinary tract anomalies were the most common associated abnormalities followed by diaphragmatic hernia or eventration. Other associations included skeletal muscle disorders, exomphalos, skeletal dysplasia, hydrops fetalis, trisomy 18, prolonged rupture of the membranes, intrauterine hypoxic–ischaemic brain damage, and five cases where there was evidence only of intrauterine or intrapartum hypoxia. Husain and Hessel found that 26% of fetuses, babies, and infants (18 weeks of gestation to 2 years of age) had pulmonary hypoplasia at necropsy, and in this series pulmonary hypoplasia was considered to be the immediate cause of death in 22%.2 In this study diaphragmatic hernia was the most common associated abnormality followed by prolonged rupture of the membranes, renal disorders, hydrops fetalis and chromosomal abnormality.
Aetiology and pathogenesis
In most cases pulmonary hypoplasia is secondary to an underlying abnormality. The pathogenesis of pulmonary hypoplasia is not fully understood but a normal thoracic cavity, fetal breathing movements, fetal lung liquid at positive pressure, and normal amniotic fluid volume are all required for normal lung growth in utero. Underlying abnormalities that may result in pulmonary hypoplasia can therefore be divided into:
space occupying lesions in the chest, such as misplaced abdominal organs in congenital diaphragmatic hernia (CDH), congenital cystic adenomatoid malformation (CCAM), and pleural effusions;
malformations of the chest wall resulting in a small thoracic cavity, as may occur in kyphoscoliosis and some skeletal dysplasias;
oligohydramnios which may result from lack of functioning renal tissue (bilateral renal agenesis or cystic dysplasia), urinary outflow obstruction, or prolonged premature rupture of the membranes;
neuromuscular disorders which prevent normal fetal breathing movements.
Primary pulmonary hypoplasia is very rare, but occasionally structurally …