Congenital Bronchopulmonary Malformations

Congenital Pulmonary Airway Malformation

CPAMs are the most commonly diagnosed BPM. Prior to the appearance of reliable prenatal imaging, the incidence of CPAM in the general population was inaccurately calculated by the postnatal identification of symptomatic lesions later in life. Large series of pregnancies evaluated prenatally by US have recently shown a probable incidence of CPAM of about 1.5 cases per 10,000 live births. This heterogeneous group of congenital cystic and noncystic lung masses is characterized by an overgrowth of immature primary bronchioles localized at a particular segment of the bronchial tree ( Fig. 22.2 ). The current classification system divides CPAMs into five types that differ by location, cystic structure, size, and epithelial lining ( Table 22.1 ). However, from a practical perspective, CPAMs can be divided into two categories based on prenatal US findings: (1) macrocystic lesions containing a dominant cyst or multiple cysts that are ≥5.0 mm in diameter and (2) microcystic lesions presenting as a solid echogenic mass ( Fig. 22.3 ).

On prenatal US, early in gestation CPAMs appear as hyperechogenic areas, with or without hypoechoic cysts, that vary in number and size. Large lesions can cause a mass effect on surrounding structures. This is seen on US images as mediastinal shift, diaphragmatic eversion, and, in the most severe cases, hydrops fetalis (e.g., polyhydramnios, ascites, pleural effusions). Pure CPAMs receive their vascular supply from the pulmonary artery and have pulmonary venous drainage. However, there is a subset of CPAMs that receive additional blood supply from a single or multiple systemic feeding vessels, which is usually considered one of the distinctive features of BPS. The systemic vessels can be one or more, and are generally branches of the abdominal aorta ( Fig. 22.4 ). CPAMs that have this feature are called hybrid lesions because of the overlapping features of CPAM and BPS. Even though the diagnosis of a CPAM by an experienced sonographer is usually straightforward, sometimes there can be confusion with other conditions ( Table 22.2 ). A skilled sonographer can usually differentiate these other lesions by understanding the blood supply (congenital diaphragmatic hernia [CDH], lung agenesis, BPS), by detecting bowel peristalsis (CDH), by documenting the absence of one lung (lung agenesis), or by detecting bronchial dilation (bronchial atresia, congenital high airway obstruction syndrome [CHAOS]).

Bronchopulmonary Sequestration

BPS comprise approximately 10% of prenatally diagnosed BPMs and are defined as a portion of lung parenchyma that does not communicate with the normal tracheobronchial tree. These lesions have a systemic arterial blood supply and may have systemic and/or pulmonary venous return. Two different types of sequestration are described: intralobar (iBPS) and extralobar (eBPS), which differ in their prenatal and postnatal characteristics. iBPS share the visceral pleural investment with the normal adjacent lung and have their venous return to the pulmonary veins. In contrast, eBPSs have a separate pleural investment and may have systemic and/or pulmonary venous drainage.

EBPSs are seen as a homogeneous hyperechoic mass in a paraspinal location most often in the left lower thorax, although they can be right-sided, mid or upper thoracic, and even intra-abdominal ( Fig. 22.5 ). The pathogenesis is related to a supernumerary lobe developing from abnormal budding early in foregut embryogenesis. If the bud arises before the development of the pleura, it is invested with the adjacent lung and becomes an iBPS. If the bud develops after visceral pleural formation, it grows separately and turns into an eBPS. EBPSs can contain CPAM components on histology ( Fig. 22.6 ). In contrast to eBPSs, iBPS have pulmonary venous drainage and are uniformly associated with the lower lobes. They are distinguishable from hybrid lesions by the absence of cysts and the presence of pulmonary arterial inflow in addition to their systemic arterial inflow. Prenatally, careful Doppler US identification of the arterial inflow to these lesions is required to distinguish between a microcystic hybrid CPAM and an iBPS. Postnatal contrast-enhanced computed tomography (CT) should be obtained in all patients to confirm the anatomy and to aid in the management. The final diagnosis will depend on histologic analysis and is frequently a combination of the classifications previously described.

Congenital Lobar Emphysema

CLE is a condition characterized by overinflation and distension of one or more pulmonary lobes secondary to a one-way-valve mechanism, with variable degrees of compression of the adjacent lung ( Fig. 22.7 ). In half the cases, the cause is unknown. In the remaining half, the overdistention results from dysplastic and weakened bronchial cartilage; endobronchial obstruction; extrinsic compression from vascular structures, cysts, tumors, etc.; or diffuse bronchial abnormalities related to infection. In the fetus, amniotic fluid trapping is analogous to postnatal air trapping, and can lead to lobar expansion. The left upper lobe is the most frequently affected, followed by right middle and upper lobes, with rare bilateral or multifocal involvement. Most neonates/infants present with respiratory distress.