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Pulmonary Hypoplasia - Types, Diagnosis, and Management

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Pulmonary hypoplasia is the presence of bronchi and alveoli in an underdeveloped lobe.

Medically reviewed by

Dr. Kaushal Bhavsar

Published At February 8, 2023
Reviewed AtMarch 20, 2024

Introduction

Pulmonary hypoplasia is a rare congenital anomaly of the lungs characterized by underdeveloped lungs. As the lungs are underdeveloped, there is a decrease in airways and alveolar sacs, resulting in impaired gaseous exchange and postnatal respiratory distress. It is commonly associated with a high neonatal mortality rate.

Reduced alveolar size and number of alveoli with a proportional decrease in the pulmonary vasculature characterize severe pulmonary hypoplasia. The risk factors associated with pulmonary hypoplasia are premature rupture of the membrane, a latency period of more than six days, and an amniotic fluid index of less than two cm.

There may be associated abnormalities of growth factors like fibroblast growth factor, epidermal growth factor, vascular endothelial growth factor, or transcription factors such as thyroid transcription factor one (TTF -1) and fibroblast growth factor seven and ten (FGF 7 and 10). Mutations in these factors may result in pulmonary hypoplasia.

How Does Lung Development Take Place?

The respiratory system is derived from the second part of the foregut. The lungs develop at the beginning of the fourth week or first month of intrauterine life. It starts as a laryngotracheal groove on the ventral aspect of the foregut, which deepens and forms a respiratory diverticulum.

The respiratory diverticulum bifurcates into right and left bronchial buds on day twenty-sixth. Asymmetric branching occurs during the following two weeks to form secondary bronchi—three on the right and two on the left, including the main divisions of the bronchial tree. The lung bud and its subsequent branches are of endodermal origin.

They give rise to the epithelium lining all the respiratory passages, the alveoli, and the associated glands. The surrounding mesoderm, the splanchnopleure, gives rise to all the supporting structures, including the connective tissue, cartilage, muscle, and blood vessels.

What Are the Types of Abnormal Lung Development?

The types of lung agenesis include:

  • Type 1 or Agenesis: Complete absence of lung, bronchus, and vascular supply on the affected side.

  • Type 2 or Aplasia: Complete absence of lungs with a rudimentary bronchus.

  • Type 3 or Hypoplasia: Partial existence of lung, bronchial tree, and vascular supply.

What Are the Types of Pulmonary Hypoplasia?

Pulmonary hypoplasia is of two types, depending on:

  • Primary pulmonary hypoplasia.

  • Secondary pulmonary hypoplasia.

Primary pulmonary hypoplasia:

It is a rare congenital anomaly caused by a primary process in which the lungs fail to form normally.

Secondary pulmonary hypoplasia:

  • Masses that compress the lung tissue, for example, congenital diaphragmatic hernia.

  • Skeletal malformations that do not allow growth of the lungs, for example, thanatophoric dysplasia.

  • Severe oligohydramnios is when fluid volume within the amniotic sac is lower than normal, usually because the placenta is not functioning properly.

What Are the Clinical Presentations of Pulmonary Hypoplasia?

In the neonatal period, pulmonary hypoplasia is lethal. Often apparent are associated congenital abnormalities. An abnormal chest radiograph in an adult can be the first presentation, occasionally. The pulmonary function tests can demonstrate obstructive or restrictive patterns and reduced diffusion capacity.

What Are the Signs and Symptoms of Pulmonary Hypoplasia?

The signs and symptoms may vary depending on the type of pulmonary hypoplasia. It includes the following:

  • Dyspnea or breathing difficulty.

  • Sunken chest.

  • Cyanosis, or reduced oxygen levels in the blood, leads to bluish skin and mucous membrane discoloration.

What Is the Histopathological Feature of Pulmonary Hypoplasia?

A characteristic feature of pulmonary hypoplasia is the lung-to-body weight ratio. The ratio is 0.012 in infants over twenty weeks of gestation, whereas in the younger fetus, the balance is 0.015. It is one of the most commonly used methods.

The disadvantage is that it can be easily affected by pulmonary edema or congestion. Another method for detecting pulmonary hypoplasia is the radial alveolar count (RAC). It is the number of alveoli crossing a line drawn from the centriole of a respiratory bronchiole to the nearest connective tissue septum.

What Are the Diagnostic Tests to Be Carried Out?

The diagnostic tests to be carried out are

Chest Radiography: It typically reveals the following:

  • Opaque hemithorax with rib crowding.

  • Ipsilateral mediastinal shift.

  • Compensatory hyperinflation of the contralateral lung.

Computed Tomography (CT) Scan: It is a confirmatory diagnostic test for pulmonary hypoplasia. It also helps to differentiate similar syndromes, such as Swyer-James syndrome and atelectasis. The typical features seen on a CT are:

  • Absent or rudimentary bronchus and underlying pulmonary vasculature.

  • Collapsed lungs on the affected side.

Ventilation-Perfusion Scan: It shows a lack of ventilation and perfusion in the affected side with significant impairment in perfusion, leading to a mismatched perfusion defect.

What Is the Management of Pulmonary Hypoplasia?

The treatment plan depends on the size of the lungs and the etiology of pulmonary hypoplasia. Management should begin in the antenatal period. Corticosteroids are administered for fetal lung maturation in fetuses over 24 weeks of intrauterine life. The ratio of lecithin to sphingomyelin is more than two in the amniotic fluid, indicating a low risk of fetal distress.

A combination of corticosteroids, antibiotics, and tocolytics is frequently administered.

Surgical procedures involving congenital repair are delayed by two to three days after birth to allow time for cardiopulmonary stability. Timing for surgical repair in a patient on extracorporeal membrane oxygenation (ECMO) immediately following birth is highly variable, but a delayed approach reduces morbidity and increases survival chances. ECMO helps with breathing.

Conclusion:

Pulmonary hypoplasia is a rare congenital anomaly of the lungs characterized by underdeveloped lungs. As the lungs are underdeveloped, there is a decrease in airways and alveolar sacs, resulting in impaired gaseous exchange and postnatal respiratory distress. A characteristic histologic feature of pulmonary hypoplasia is the ratio of the lung to body weight (LW:BW).

The treatment plan depends on the size of the lungs and the etiology of pulmonary hypoplasia. Management should begin in the antenatal period. A combination of corticosteroids, antibiotics, and tocolytics is frequently administered. Surgical procedures involving congenital repair are delayed by two to three days after birth to allow time for cardiopulmonary stability. ECMO helps with breathing as it reduces morbidity and increases survival chances.

Dr. Kaushal Bhavsar
Dr. Kaushal Bhavsar

Pulmonology (Asthma Doctors)

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