Type 3 lesions have no visible cysts, because the cysts are too small to be seen with ultrasound. When the entire lung is involved, the appearance of a type 3 cystic adenomatoid malformation is the same as that of bronchial atresia.
Color Doppler can be used to determine that the blood supply to the mass arises from the pulmonary artery (Figure 8.1.4). Sometimes, the cystic lung mass will decrease in size during gestation (Figure 8.1.5). If the cystic adenomatoid malformation is large, it may cause mediastinal shift or inversion of the diaphragm, and the fetus may have ascites, pleural effusions, or full-blown hydrops (Figure 8.1.6).
A sequestration appears on ultrasound as a homogeneously echogenic mass located either within the thorax (Figure 8.1.7) or just below the diaphragm (Figure 8.1.8). Color Doppler is used to identify the feeding artery from the aorta (Figure 8.1.9), confirming the systemic blood supply. This finding helps distinguish a sequestration from a type 3 (microcystic) cystic adenomatoid malformation of the lung, which receives its blood supply from the pulmonary artery.
Mixed pulmonary lesions, those with characteristics of both cystic adenomatoid malformation and sequestration, appear as cystic lung masses with systemic arterial blood supply (Figure 8.1.10).
8.2. Tracheal and Bronchial Atresia
Description and Clinical Features
If the trachea is atretic, pulmonary secretions remain trapped behind the atresia in the lungs. This leads to distention of the lungs. The distended lungs compress the heart, preventing adequate venous return and causing hydrops. Tracheal atresia is likely to be fatal at birth. Even if the condition is diagnosed prenatally, establishing an airway at delivery may be impossible.
Atresia of a bronchus will lead to distention of one lung, causing mass effect, with shift of the heart and mediastinum to the contralateral side. The lung distal to the obstruction develops abnormally. The condition falls under the spectrum of pulmonary dysplasias, as it is similar or identical to cystic adenomatoid malformation type 3 involving the entire lung.
Sonography
With tracheal atresia, both lungs are large and homogeneously echogenic (Figure 8.2.1) due to excessive fluid within them and multiple interfaces between fluid and soft tissues. The heart appears relatively small within the thorax, compressed by lungs. Both hemidiaphragms are inverted due to hyperexpansion of the lungs. The bronchi are typically dilated, and may be identifiable as distended fluid-filled tubular structures within the lungs. Fetal hydrops may be present.
When bronchial atresia is present, the affected lung is large and homogeneously echogenic (Figure 8.2.2). The heart is displaced to the contralateral side.