Bronchopulmonary sequestration (BPS) is a mass of nonfunctioning pulmonary tissue that lacks an obvious communication with the tracheobronchial tree and receives all or most of its blood supply from anomalous systemic vessels (Carter, 1959). There appears to be a spectrum of sequestration with, at one extreme, an abnormal vessel supplying a nonsequestered lung and, at the other extreme, abnormal pulmonary tissue but without anomalous vascular supply. Terminology has become increasingly complicated with terms such as congenital bronchopulmonary foregut malformation (CBPFM) and malinosculation used (Gerle et al., 1968; Heithoff et al., 1976; Clements and Warner, 1987). CBPFM refers to intralobar or extralobar BPS associated with a communication with the gastrointestinal tract. The spectrum of CBPFM includes intralobar sequestration, extralobar sequestration, congenital cystic adenomatoid malformation (CCAM), bronchogenic cyst, Scimitar syndrome, and duplication cyst. Malinosculation describes the spectrum of congenital lung anomalies, in which there is abnormal connection of one or more of the four major components of the lung tissue (Clements and Warner, 1987). While much emphasis has been placed in the past in differentiating between BPS and CCAM, it is now clear that both can coexist in the same lesion, where it is referred to as a hybrid lesion. Extralobar sequestration and CCAM type II coexisting together has been reported in 25% to 50% of extralobar sequestration cases (Conran and Stocker, 1999) (see Chapter 35).

There are two forms of BPS: intralobar and extralobar. Intralobar is the more common malformation seen in infants and children, accounting for 75% of cases of BPS, and it shares the same pleural investment with the normal lung (Savic et al., 1979; Collin et al., 1987). Extralobar BPS accounts for 25% of cases in infants and children, has a separate pleura from the lung, and may be either intrathoracic or subdiaphragmatic in location (Savic et al., 1979; Collin et al., 1987).

The most widely accepted theory about the embryogenesis of BPS is that a supernumerary lung bud arises caudal to the normal lung bud and migrates caudally with the esophagus. If this lung bud arises prior to the development of the pleura, the bud is invested with adjacent lung and becomes an intralobar BPS. If supernumerary development occurs subsequent to pleura formation, the bud will grow separately and become invested with its own pleura, forming an extralobar BPS (Carter, 1959).

BPS is seen in 0.8% to 1.4% of all pulmonary resections (Carter, 1959). There is no familial predisposition. There is a slight male predominance, which is more obvious in extralobar BPS (male to female ratio of 3:1) compared with intralobar BPS (male to female ratio of 1.5:1) (Warner et al., 1958; Carter, 1959; Williams and Enumah, 1968). Extralobar BPS is much more common in the fetus and neonate than intralobar BPS (Buntain et al., 1977; Moulik et al., 1987; Panicek et al., 1987; Felker and Tonkin, 1990; Sauerbrei, 1992).

Intralobar BPS is located within the lower lobe in 98% of cases. Extralobar BPS is usually located in the posterior lower chest and 90% of extralobar BPS is located on the left side. Up to 15% of extralobar BPS can be found either within or below the diaphragm (Berrocal et al., 2004).

BPS is a solid, highly echogenic mass (Figure 34-1) with a clearly defined systemic feeding vessel (Figure 34-2). There have now been many reports of the prenatal sonographic diagnosis of BPS (Newman, 1970; Jaffe et al., 1982; Romero et al., 1982; Jouppila et al., 1983; Kritstoffersen and Ipsen, 1984; Mariona et al., 1986; Thomas et al., 1987; Adzick et al., 1998; Baumann et al., 1988; Davies et al., 1989a; Morin et al., 1989; Siffling et al., 1989; Weinbaum et al., 1989; Slotnick et al., 1990; Stern et al., 1990; Boiskin et al., 1991; Heranz-Schulman et al., 1991; Dolkhart et al., 1992; Eisenberg et al., 1992; Sauerbrei, 1992; Luetic et al., 1995). The sonographic hyperechogenicity of BPS is thought to result from the interfaces created by numerous dilated bronchioles (Jaffe et al., 1982). The demonstration of the systemic blood supply to the mass by color Doppler sonography usually confirms the diagnosis (Figures 34-2 to 34-4). Occasionally, these vessels cannot be demonstrated sonographically, making it difficult to distinguish BPS from type III congenital cystic adenomatoid malformation (CCAM) of the lung (see Chapter 35). Even if an anomalous systemic blood supply to a thoracic mass can be demonstrated, which confirms the diagnosis of BPS, intralobar and extralobar BPS usually cannot be distinguished by prenatal ultrasound. Several cases of extralobar BPS have been reported prenatally because of the finding of echogenic suprarenal abdominal masses (Mariona et al., 1986; Baumann et al., 1988; Davies et al., 1989b; Dolkhart et al., 1992).

Additional sonographic findings seen in association with BPS include pleural effusion, mediastinal shift, hydrops, and polyhydramnios (Morin et al., 1989, 1994a, 1994b; Gross et al., 1992). Extralobar BPS may undergo torsion of its vascular pedicle, causing venous and lymphatic obstruction, leading to pleural effusion and hydrops due to systemic venous obstruction (Vode and Kramer, 1989; Morin et al., 1994a). Fetal hydrops may result from a compressive effect of the sequestration on the inferior vena cava with venous obstruction and compromised cardiac output. Polyhydramnios may be seen in association with BPS due to esophageal obstruction or decreased swallowing. BPS associated with hydrops uniformly results in fetal or neonatal death if untreated. There have been anecdotal reports of cases treated successfully in utero by thoracoamniotic shunting of the associated pleural effusion. To date, open fetal surgery has not been reported for a BPS in contrast to hybrid CCAM (see Chapter 35).

In postnatal series of BPS, there is a high incidence of associated anomalies, especially in extralobar BPS (60% of cases) (Warner et al., 1958; Carter, 1959; Gerle et al., 1968; Sade et al., 1974; Buntain et al., 1977; Savic et al., 1979; Collin et al., 1987). The most commonly associated anomalies include congenital diaphragmatic hernia (CDH), pectus excavatum, tracheoesophageal fistula, esophageal duplication, and congenital heart disease (Warner et al., 1958; Carter, 1959; Gerle et al., 1968; Buntain et al., 1977). The intralobar type has a lower incidence of associated anomalies (10% of cases) (Carter, 1959; Gerle et al., 1968; Sade et al., 1974; Buntain et al., 1977).

The differential diagnosis of intrathoracic BPS includes type III CCAM, mediastinal or thoracic teratoma, and CDH (Moulik et al., 1987; Morin et al., 1994a) (Table 34-2). Type I or II CCAMs have a characteristic cystic appearance that clearly distinguishes them sonographically from BPS, while type III CCAMs have a dense hyperechoic appearance that may be indistinguishable from BPS. Mediastinal teratomas usually have a higher density, causing acoustic shadowing behind the mass (Golladay and Mollitt, 1984). Prenatal diagnosis of BPS may be quite difficult. In a review of cases diagnosed antenatally, only 29% were diagnosed correctly (Dolkhart et al., 1992). The other cases of BPS were documented variously as tumor, diaphragmatic hernia, CCAM, neuroblastoma, collapsed lung, and abdominal mass (Siffling et al., 1989; Dolkhart et al., 1992). The distinction between CCAM and BPS when a systemic feeding vessel is not demonstrated usually comes down to the echotexture of the mass. The presence of cysts suggests CCAM, whereas solid triangular lesions are more consistent with BPS, especially in the lower thoracic region. In lesions that are without cysts, it may not be possible to distinguish type III hybrid CCAM from BPS.