This is failure of development of the lungs in utero, which is most often unilateral and can range from hypoplasia to aplasia (agenesis). The end result is lungs that do not have enough tissue and blood flow for adequate gas exchange.
Pulmonary agenesis is the complete absence of lung tissues, bronchi, and pulmonary vessels, which may be unilateral or bilateral. The right-sided form carries the poorest prognosis due to severity of co-existent anomalies. Antenatal diagnosis using fetal ultrasound and MRI allows early diagnosis. Differential diagnoses include diaphragmatic hernia, cystic adenomatoid malformation of the lung, giant lobar emphysema, and situs inversus. Pulmonary agenesis may be compatible with normal life provided co-existent malformations are thoroughly investigated and managed.
Primary isolated bilateral pulmonary hypoplasia is rare and familial occurrence exceptional.
Pulmonary hypoplasia occurs commonly in association with congenital diaphragmatic hernia, oligohydramnios (mostly related to renal dysfunction), skeletal dysplasias, fetal hydrops, malformations of the central nervous system and neuromuscular diseases.
Pulmonary agenesis is a rare congenital anomaly, which occurs in about 1 per 15,000 pregnancies. There is complete absence or severe hypoplasia of one or both lungs, often associated with other abnormalities.
Normal lung growth requires the following:
- Normal thoracic cavity.
- Normal fetal breathing movements.
- Normal amniotic fluid volume.
- Fetal lung liquid at the right pressure.
This can therefore be caused by:
- Abnormal thoracic cavity: congenital diaphragmatic hernia (in this situation the bowel and stomach are sitting in the chest cavity) or malformations of the chest cavity.
- Abnormal fetal breathing movements: neuromuscular disease in utero can result in decreased fetal breathing movement - eg, central nervous system (CNS) lesions or space-occupying lesions.
- Abnormal amniotic fluid volume: oligohydramnios - due to renal agenesis or urinary outflow obstruction or prolonged rupture of membranes.
- Abnormalities of fetal lung fluid and lung fluid pressure: the underlying pathophysiology which results in abnormal lung fluid pressure and subsequent pulmonary hypoplasia is unclear.
There is probably an overlap of aetiologies. However, pulmonary hypoplasia may also be idiopathic or related to other syndromes and congenital anomalies - eg, multiple pterygium syndrome/fetal akinesia-hypokinesia sequence (autosomal recessive)/scimitar syndrome and trisomy 21.
Congenital lung abnormalities are increasingly detected at the time of routine high-resolution prenatal ultrasound.
- Immediate difficulty in breathing with respiratory distress - eg, cyanosis, intercostal recession with tachypnoea, acid base disturbance (acidosis, hypoxia and hypercarbia).
- There may be features of other fetal disorders - eg, skeletal dysplasia or 'Potter's facies' in oligohydramnios.
- Other congenital anomalies - eg, cardiac malformations.
- Suspect if oligohydramnios is present.
- Fetal ultrasonography - can be used to measure lung area to head circumference ratio; a ratio of <1 is associated with high rate of neonatal death. Doppler velocimetry has been used experimentally and can detect severe hypoplasia.
- Increased nuchal translucency is seen in almost half of fetuses who have a congenital diaphragmatic hernia.
- Suspect pulmonary hypoplasia in any neonate with immediate respiratory distress.
- Resuscitation: airway, breathing and circulation. Neonates should be resuscitated for up to several hours.
- Neonates will need to be intubated and ventilated (increased risk of pneumothorax).
- If a congenital diaphragmatic hernia is suspected then ventilation can worsen respiratory distress (decompression of the stomach and bowel is required).
- Measurement of blood gases - usually via umbilical artery catheterisation.
- Correction of the underlying cause - eg, surgical repair of a diaphragmatic hernia.
Methods to correct pulmonary hypoplasia in utero
Fetal endoscopic tracheal occlusion has been used in humans to treat congenital diaphragmatic hernia and pulmonary hypoplasia with some success.
This depends on the degree of hypoplasia, the underlying cause and other associated congenital abnormalities.
Survivors often have chronic lung problems - eg, reduced lung capacity, recurrent chest infections and impaired growth.
Severe pulmonary hypoplasia and pulmonary arterial hypertension are associated with reduced survival in babies with congenital diaphragmatic hernia.
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