Pulmonary Hypoplasia

Chapter 16

Pulmonary Hypoplasia

Brian P. O’Sullivan, MD

Introduction/Etiology/Epidemiology

•Pulmonary hypoplasia is arrested or impaired growth and development of the lung, airways, and pulmonary vessels.

•Overall incidence is 9–11 cases in 10,000 live births.

•Pulmonary hypoplasia may be primary or secondary, unilateral or bilateral.

—Primary pulmonary hypoplasia and familial occurrences are extremely rare.

—Secondary pulmonary hypoplasia is caused by a process that limits the space for lung development.

—The most common intrathoracic cause is congenital diaphragmatic hernia.

—The most common extrathoracic cause is severe oligohydramnios secondary to either genitourinary anomalies or midtrimester rupture of membranes.

—Pulmonary agenesis is an extreme variant.

▪Bilateral agenesis is incompatible with life.

▪Unilateral agenesis occurs with pulmonary artery agenesis or pulmonary venous anomalies (Figure 16-1).

▪Agenesis of the right lung is associated with respiratory symptoms caused by a mediastinal shift to the right, with distortion of major vessels and airways.

•Variations in bronchopulmonary vasculature are common.

•Associated anomalies of the diaphragm, heart, gastrointestinal tract, and bone occur at increased rates.

Pathophysiology

The following etiologic origins have been proposed:

•Pulmonary artery agenesis and/or anomalous venous drainage

—Pulmonary artery agenesis is a common cause of complete pulmonary agenesis.

—Scimitar syndrome consists of hypoplasia of the right lung with abnormal venous drainage to the inferior vena cava (Figure 16-2).

—Scimitar syndrome can be an asymptomatic incidental finding in adults but is often associated with severe cardiac defects, anomalous systemic arterial supply to the right lung, and pulmonary vein stenosis.

Figure 16-1. Frontal chest radiograph of a 1-month-old female infant with left pulmonary agenesis. Note the displacement of the heart and mediastinum into the left axillary line and herniation of the right lung into the left chest cavity (arrows).

•Chest wall abnormalities

—Skeletal abnormalities that affect the chest wall and/or rib growth or position will restrict lung growth and lead to hypoplasia (eg, thanatophoric dysplasia, achondroplasia).

•Absent or disordered fetal breathing movements

—Fetal breathing movements are imperative for normal lung development.

—Lack of fetal breathing movements inhibits alveolar development.

—This symptom can be caused by central nervous system abnormalities or phrenic nerve injury or agenesis.

•Amniotic fluid abnormalities

—Fetal urination is the primary source of amniotic fluid.

—Normal net movement of lung liquid is out of the lung and into the amniotic cavity, not movement of amniotic fluid into the lungs.

—Oligohydramnios causes pulmonary hypoplasia because of compression of the chest wall by the maternal uterine wall and/or excess flow of fluid out of the lungs and into the amniotic cavity secondary to decreased amniotic fluid pressure.