Embryology · Respiratory system, diaphragm and body cavities

Pulmonary hypoplasia !

Malformation

The lungs end up small, with few branches and air sacs, because something took away their room or their fluid during pregnancy.

Updated 2026-11-01

See it in 3D: Main bronchi · Pulmonary arteries · Kidneys

What it is

Pulmonary hypoplasia is a lung with fewer cells, airways, alveoli and vessels than normal. It is nearly always secondary: too little room in the chest, too little amniotic fluid or too few fetal breathing movements during the second trimester. It is the main cause of death in congenital diaphragmatic hernia and in the Potter sequence.

Embryological cause

The fetal lung needs room, fluid in the airways and breathing movements to branch.
Compression: diaphragmatic hernia, pleural effusion, hydrops or a small chest from skeletal dysplasias.
Oligohydramnios: without fluid the chest is squeezed and lung fluid escapes, which stalls growth.
Absent breathing movements: neuromuscular or fetal nervous system disease.
If the insult falls in the pseudoglandular and canalicular stages, fewer bronchial generations, alveoli and vessels form.

How it presents

Severe respiratory failure from birth, with a small chest.
Spontaneous pneumothorax or pneumothorax during ventilation.
Persistent pulmonary hypertension of the newborn.
In the Potter sequence: flattened face, low-set ears and limb deformities.

Diagnosis

Prenatal: low lung-to-head ratio on ultrasound and reduced lung volume on fetal MRI.
X-ray: small chest and poorly expanded lungs.
Autopsy: low lung weight relative to body weight and a reduced radial alveolar count.

Test yourself

Think of the answer, then tap the question to see it.

What are the three main mechanisms of pulmonary hypoplasia?

Chest compression (for example diaphragmatic hernia), oligohydramnios and absent fetal breathing movements.

In which stages of lung development is the lung most vulnerable to hypoplasia?

The pseudoglandular and canalicular stages, weeks 5 to 26, when bronchial branches and vessels form.

Why does bilateral renal agenesis cause pulmonary hypoplasia?

Because with no fetal urine there is severe oligohydramnios; the chest is compressed and the lung loses the fluid it needs to grow.

Which vascular complication comes with pulmonary hypoplasia?

Persistent pulmonary hypertension, because the lung's vascular bed is small.

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See it in 3D

The structures of Durgical's 3D anatomy where it is found.

← All of embryology

Educational content on embryonic development; not a guide to prenatal diagnosis or to medicines in pregnancy and no substitute for a health professional's advice. No doses are given.

Sources: Potter syndrome: MedlinePlus Medical Encyclopedia (MedlinePlus, U.S. National Library of Medicine, 2025); Congenital diaphragmatic hernia: MedlinePlus Genetics (MedlinePlus, U.S. National Library of Medicine, 2019); Langman's Medical Embryology, 13th ed., ch. 14: Respiratory System (Wolters Kluwer, 2015).

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Representative model, for educational purposes only.