Causes
Causes of pulmonary hypoplasia include a wide variety of congenital malformations and other conditions in which pulmonary hypoplasia is a complication. These include congenital diaphragmatic hernia, congenital cystic adenomatoid malformation, fetal hydronephrosis, caudal regression syndrome, mediastinal tumor, and sacrococcygeal teratoma with a large component inside the fetus. Large masses of the neck (such as cervical teratoma) also can cause pulmonary hypoplasia, presumably by interfering with the fetus's ability to fill its lungs. In the presence of pulmonary hypoplasia, the EXIT procedure to rescue a baby with a neck mass is not likely to succeed.
Fetal hydrops can be a cause, or conversely a complication.
Pulmonary hypoplasia is associated with oligohydramnios through multiple mechanisms. Both conditions can result from blockage of the urinary bladder. Blockage prevents the bladder from emptying, and the bladder becomes very large and full. The large volume of the full bladder interferes with normal development of other organs, including the lungs. Pressure within the bladder becomes abnormally high, causing abnormal function in the kidneys hence abnormally high pressure in the vascular system entering the kidneys. This high pressure also interferes with normal development of other organs. An experiment in rabbits showed that PH also can be caused directly by oligohydramnios.
Pulmonary hypoplasia is associated with dextrocardia of embryonic arrest in that both conditions can result from early errors of development, resulting in congenital cardiac disease.
PH is a common direct cause of neonatal death resulting from pregnancy induced hypertension.
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