Causes of Pulmonary Hypoplasia

By Sally Robertson, B.Sc.Reviewed by Dr. Catherine Shaffer, Ph.D.

Pulmonary hypoplasia is a condition where a baby’s lungs have failed to develop properly during development in the womb. The alveoli, which are needed for the exchange of oxygen and carbon dioxide in the lung, are reduced in number, which affects the baby’s ability to breathe independently after birth. If newborns with pulmonary hypoplasia cannot be supported long enough for new lung tissue to grow, they are at risk of developing lung failure.

Causes

Pulmonary hypoplasia usually occurs as a secondary problem to another health condition that limits lung development. The condition is therefore usually referred to as secondary pulmonary hypoplasia. The most common causes are listed below:

Oligohydramnios (insufficient amniotic fluid)

Oligohdramnios is one of the most common conditions associated with pulmonary hypoplasia. It is most often caused by early leaking of the amniotic fluid as a result of premature membrane rupture. When fluid is lost from around the baby, the movement of the chest wall as the baby breathes becomes restricted. Fetal breathing and sufficient pressure of the amniotic fluid are essential for normal fetal lung development.

The second most common cause of oligohydramnios is fetal renal abnormality. Aside from the amniotic membranes, the fetal kidneys produce amniotic fluid. Abnormalities such as polycys tic kidneys or renal agenesis (where one or both kidneys fail to develop) can result in too little fluid being formed.

Congenital Conditions

Structural problems during development that occur as a result of certain congenital conditions may also impair lung growth. Examples include the following:

Congenital diaphragmatic hernia

In congenital diaphragmatic hernia, the development of the diaphragm is inadequate. ,The diaphragm separates the lung and abdomen. This results in a hole in the diaphragm that may be one to several inches wide. Some of the contents of the abdomen such as the small intestine, spleen or liver then move into the chest cavity, where they can restrict lung growth and development.

Dwarfism

Certain forms of dwarfism are associated with abnormalities that limit the space needed for normal lung growth. The condition thanatophoric dwarfism, for example, is characterized by abnormalities in the shape, size and density of bones. This results in short limbs and an enlarged head, as well as other features of the disease including a narrow chest, short ribs and underdeveloped lungs.

Cystic hygroma

A cystic hygroma is a fluid-filled sac (cyst) that often develops on a baby’s head or neck due to an abnormally formed lymphatic system. Cystic hygroma on the neck can start to interfere with breathing, as the cyst fills with fluid and puts pressure on the respiratory airways.

Cystic adenomatosis malformation

The lungs are made up of five lobes, with two found on the left lung and three found on the right lung. In cystic adenomatosis malformation, faulty development of one of the lobes results in the formation of a cyst in the lobe rather than normal lung tissue. This is the most common type of lung lesion found in the fetus.

Hydrops fetalis

In hydrops fetalis , severe and life threatening edema (swelling) develops as fluid builds up and surrounds the lungs, abdomen and heart of the fetus.

Primary Pulmonary Hypoplasia

Primary pulmonary hypoplasia is very rare, but, occasionally, the baby’s lungs are found to be hypoplastic (underdeveloped), despite being structurally normal and no underlying cause can be identified.

Further Reading

• All Pulmonary Hypoplasia Content
• Lung Hypoplasia: Management and Prognosis
• Pulmonary Hypoplasia: Overview