Bronchopulmonary sequestration

INTRODUCTION — Bronchopulmonary sequestration (BPS), sometimes referred to simply as pulmonary sequestration, is a rare congenital abnormality of the lower airway. It consists of a nonfunctioning mass of lung tissue that lacks normal communication with the tracheobronchial tree and that receives its arterial blood supply from the systemic circulation [1].

BPS can present in several ways. Extralobar BPS is often identified on prenatal ultrasound and becomes symptomatic early in life, whereas intralobar BPS is more commonly identified later in life secondary to recurrent infection.

The postnatal presentation and management of BPS will be discussed below. Prenatal manifestations and management are described in a separate topic review. (See "Bronchopulmonary sequestration: Prenatal diagnosis and management".)

DEFINITIONS — BPS is a nonfunctioning mass of lung tissue, with airway and alveolar elements, that lacks normal communication with the tracheobronchial tree and receives its arterial blood supply from the systemic circulation. The subtypes are classified anatomically, as follows:

●Intralobar sequestration (ILS) – An ILS (also known as intrapulmonary sequestration) is located within a normal lobe and lacks its own visceral pleura. ILS accounts for approximately 75 percent of BPS.

●Extralobar sequestration (ELS) – An ELS (also known as extrapulmonary sequestration) is located outside the normal lung and has its own visceral pleura. Occasionally, it is located below the diaphragm [2]. ELS accounts for approximately 25 percent of BPS and is more likely to be associated with other congenital anomalies.

●Hybrid BPS/congenital pulmonary airway malformation (CPAM) lesions – In a hybrid lesion, BPS (either ILS or ELS) occurs in combination with a CPAM. These hybrid lesions have histologic features of CPAM, have a blood supply from a systemic artery, and have been reported in a substantial proportion of cases of BPS [3,4]. (See "Congenital pulmonary airway malformation".)

●Bronchopulmonary foregut malformation – This term is usually used to refer to a rare variant of sequestration in which the sequestered lung tissue is connected to the gastrointestinal tract [5]. This may occur in either ILS or ELS. Occasionally, bronchopulmonary foregut malformation is used as a general term to include all foregut malformations.

EPIDEMIOLOGY — Congenital abnormalities of the lower respiratory tract are rare, found in approximately 1 in 10,000 to 35,000 live births [4]. Among these, the most common is congenital pulmonary airway malformation (CPAM), while BPS represents only 0.15 to 6.40 percent [6]. In several reports, even tertiary care referral centers diagnose less than one case per year of BPS [7-10].

Intralobar sequestration (ILS) is overall the most common form, comprising approximately 75 to 90 percent of sequestrations, while 10 to 25 percent are extralobar sequestration (ELS) [6,11]. The difference in prevalence of the disorders may be related to the pathogenic mechanisms, as discussed below. Males and females are equally affected with ILS, while ELS has a male predominance in most [1,10], but not all [3], reports. In a series of ELS cases diagnosed antenatally, the ratio of males to females was three to one [12,13]. In contrast, bronchopulmonary foregut malformation has a female predominance [5].

PATHOGENESIS — The embryologic basis for the development of BPS and other congenital abnormalities of the lower airway are not fully understood [5,14]. The most widely accepted embryologic theory is that BPS originates early in the pseudoglandular stage of lung development (5 to 17 weeks of gestation), prior to separation of the aortic and pulmonary circulations [15]. This would explain the wide spectrum of pathology observed, including the connections to the systemic circulation, the presence of separate visceral pleura in extralobar sequestration (ELS) or lack thereof in intralobar sequestration (ILS), the occurrence of hybrid lesions with features of BPS and congenital pulmonary airway malformation (CPAM), and the occasional associations with bronchogenic cysts or connections to the foregut, as well as associated anomalies such as congenital diaphragmatic hernia [15-17]. In utero airway obstruction may contribute to some of the morphologic changes [18].

Another proposed explanation is that a portion of the developing lung is mechanically separated from the rest of the organ by compression from vascular structures, traction by aberrant systemic vessels, or inadequate pulmonary blood flow. However, this mechanical hypothesis does not completely explain all types of lesions, specifically bronchopulmonary foregut malformation [5,14].

In the past, ILS was proposed to be an acquired rather than a developmental lesion. This hypothesis was suggested by the late presentations of ILS in historical series and also by observations that systemic arterial collaterals (resembling BPS) occasionally develop in the setting of pulmonary inflammatory processes [19,20].

ANATOMIC CHARACTERISTICS — Sequestrations are characterized by their location, connection to pulmonary or other structures, vascular supply, and association with other abnormalities. By definition, their arterial blood supply is from the systemic circulation.

Intralobar sequestration — Intralobar sequestrations (ILS) are located within a normal lobe and lack their own visceral pleura. Most ILS occur in the lower lobes, but they can occur anywhere within the thorax [21]. Approximately 60 percent are located in the posterior basal segment of the left lower lobe [1,5,8,11,22], and rare instances of bilateral ILS (or ILS with contralateral extralobar sequestration [ELS]) have been reported [23]. They generally have no bronchial connection to the proximal airway. If a connection exists, it is abnormal. However, anomalous connections can link the sequestration to other bronchi, or lung parenchyma, and there are connections to the gastrointestinal tract in approximately 10 percent, constituting a bronchopulmonary foregut malformation [11,15]. These connections and/or the pores of Kohn may allow bacteria to enter the sequestration and cause recurrent infection, a common finding in ILS (picture 1).

The arterial supply usually is derived from the lower thoracic or upper abdominal aorta. In a series of 25 cases, 16 had a single arterial trunk and the remainder had multiple arterial vessels (image 1A-B) [24]. Venous drainage is usually normal to the left atrium, although abnormal connections to the vena cava, azygous vein, or right atrium may occur [11].

On pathologic examination, there are often changes at the pleural surface overlying the abnormal region [25]. On cut section, the parenchyma of the sequestration is usually sharply demarcated from the adjacent normal tissue. The abnormal parenchyma has enlarged airspaces and thickening of the airspace wall (picture 1). The airways of the lesion are dilated and filled with mucus, with regions of inflammation, mucus accumulation, and microcystic changes, with more distortion of the lung parenchyma than is typically seen in ELS. Sometimes, dilated lymphatic channels are associated with the lesion (picture 2). (See "Congenital anomalies of the intrathoracic airways and tracheoesophageal fistula".)

Extralobar sequestration — Extralobar sequestrations (ELS) are located outside the normal lung and have their own visceral pleura, with a pedicle that contains the vascular connections. They vary in size but usually are relatively small compared with the normal lobes. The vast majority are in the left hemithorax, and the most common location is between the left lower lobe and hemidiaphragm (80 percent) [26,27]. Occasionally, ELS may present within or below the diaphragm or in the retroperitoneum, particularly in the region of the adrenal gland where they may mimic a suprarenal neuroblastoma [28]. Like ILS, ELS lesions lack a bronchial connection to the normal proximal airway. They may connect to the gastrointestinal tract or, rarely, to intrapulmonary structures [11]. Because intrapulmonary connections are uncommon in ELS, infectious complications are also uncommon. The arterial supply of ELS usually comes from an aberrant vessel arising from the thoracic aorta [11]. The vessel is usually small, with low flow. Lesions typically have anomalous venous drainage to the right atrium, vena cava, or azygous systems [29]. On histologic examination, ELS may resemble normal lung or show parenchymal maldevelopment similar to the small-cyst type of congenital pulmonary airway malformation (CPAM) [25].

Hybrid BPS/CPAM lesions — Hybrid lesions, with features of BPS and CPAM, occur in a substantial proportion of BPS [3,30,31] and comprise 15 to 40 percent of all cystic lung lesions [32]. These lesions have blood supply from a systemic artery consistent with BPS, but they also have histologic features of CPAM. In one report, five cases of ILS and one of ELS that were diagnosed prenatally had a systemic artery detected at surgical resection, but histology was consistent with CPAM [30]. In another series, 23 of 46 cases of ELS had histologic features of CPAM type 2 [3]. Of these, 11 had rhabdomyomatous degeneration.

CLINICAL PRESENTATION — The clinical presentation of BPS is variable and depends upon the type, size, and location of the lesion. Many cases are initially detected by routine prenatal ultrasound examination. Most affected newborns are asymptomatic. If symptomatic, BPS usually presents with respiratory distress in the neonatal period. Intralobar sequestration (ILS) or hybrid forms often present later in life, with infection [1,3,5,7,8,14,22,33]. Presentation with infection is less likely with extralobar sequestration (ELS). ELS may also be diagnosed incidentally on a chest radiograph taken for other reasons.

Prenatal — On prenatal ultrasound, BPS appears as a homogenous echogenic thoracic mass, usually solid-appearing, triangular, and often located in the lower hemithorax adjacent to the diaphragm. The size of the lesion varies considerably, ranging from very small to one that occupies most of the hemithorax, causing mediastinal shift [34-38]. BPS may be difficult or impossible to distinguish from microcystic congenital pulmonary airway malformations (CPAM), unless a systemic arterial feeder can be identified (image 2). (See "Bronchopulmonary sequestration: Prenatal diagnosis and management", section on 'Prenatal diagnosis'.)

In the majority of cases, the lesion regresses during the course of gestation. Occasionally, hydrops develops, likely because of vascular compression [34,39,40]. There are no reliable criteria for determining which lesions will grow and develop hydrops versus those that will stabilize or regress [37]. Management of prenatally detected BPS including hydrops and planning the method and optimal setting for delivery are discussed separately [41]. (See "Bronchopulmonary sequestration: Prenatal diagnosis and management".)

In cases demonstrating in utero regression, postpartum imaging is still required because few lesions resolve completely. (See 'Postnatal imaging' below.)

Neonatal period — Infants with BPS or other congenital abnormalities of the lower airway may be either asymptomatic or symptomatic at birth:

●Asymptomatic – Most infants with BPS are asymptomatic at birth. The lesion may have been identified on prenatal ultrasound or identified incidentally during a postnatal evaluation for other congenital anomalies.

●Symptomatic – Some infants with prenatally diagnosed lung lesions present with respiratory distress at birth or shortly thereafter; this may occur with either ILS or ELS and is more likely if the lesion is large. The symptoms are usually due to large lesions that limit the volume of the normal lung; rarely, they are caused by high-output heart failure if the sequestration takes a large portion of the systemic arterial flow, thus creating a significant left-to-right shunt.

Postneonatal — Among infants who are asymptomatic at birth, some will become symptomatic later in infancy, childhood, or even adulthood, but the natural history and magnitude of risk is poorly delineated. (See 'Low risk' below.)

Other individuals remain asymptomatic throughout life but come to attention when the lesion is detected as an incidental finding on a chest radiograph. Unfortunately, the percentage of those who will become symptomatic is not known, because the natural history of infants who are asymptomatic at birth is not well described. As a result, the optimal management of an asymptomatic infant is also uncertain, as discussed below. (See 'Asymptomatic patients' below and "Congenital pulmonary airway malformation", section on 'Asymptomatic'.)

The most common symptomatic presentation after the neonatal period is with pulmonary infection, typically presenting with fever and cough and sometimes hemoptysis or chest pain (image 3) [33,42]. This is most likely for those with ILS, which comprise approximately 75 percent of BPS. Rare complications of either ELS or ILS include heart failure due to excessive flow through the aberrant artery [11,43], massive bleeding [44,45], or torsion [46]. Cases have been reported of fibrous mesothelioma [47] and carcinoma [25,48,49] arising within ILS. These disorders may be related to an association of ILS with CPAM. (See "Congenital pulmonary airway malformation".)

Patients with ELS are unlikely to develop infection. Those that do present with infection tend to be hybrid lesions with CPAM [3]. It is clear that some patients with ELS will remain asymptomatic throughout life, but the likelihood of this outcome is unknown.

Associated anomalies — Congenital anomalies may be associated with BPS, occurring more frequently in patients with ELS than ILS. In a series of 28 cases in children and adults, associated malformations occurred in 43 percent of ELS and 17 percent of ILS [6]. Similar proportions were seen in an older series of 540 cases [50]. Associated anomalies include congenital diaphragmatic hernia, vertebral anomalies, congenital heart disease, and colonic duplication [5,14]. Infants with a large BPS may have pulmonary hypoplasia due to mass effects in utero.

EVALUATION

Postnatal imaging — All cases of BPS or other congenital abnormalities of the lower airway should be further evaluated with imaging. This includes cases that regressed or appeared to resolve in utero because few lesions resolve completely and advanced imaging is more sensitive than prenatal ultrasound for detecting small lesions.

Suggested protocol — After birth, the first step is a plain chest radiograph. The second step is advanced imaging, the timing of which depends on the patient's characteristics, as outlined in the algorithm (algorithm 1) and discussed below:

●High risk – We suggest immediate advanced thoracic imaging with computed tomography (CT) or magnetic resonance imaging (MRI) for infants with any of the following characteristics:

•Any symptoms (eg, respiratory distress)

•Large BPS (occupying >20 percent of the hemithorax on ultrasonography or plain radiographs)

•Risk factors for pleuropulmonary blastoma (bilateral or multifocal cysts, pneumothorax, or a family history of pleuropulmonary blastoma-associated conditions (table 1))

The purpose of the advanced imaging is to confirm the diagnosis, identify the aberrant artery, and help with surgical planning [51]. Doppler ultrasonography also may be helpful to define the aberrant artery. These techniques have replaced the need for angiography to identify the vascular supply (image 1B).

●Low risk – Infants who are asymptomatic and do not have the high-risk characteristics outlined above should have advanced thoracic imaging (CT or MRI) by six months of age to confirm the diagnosis and examine further for characteristics that require surgical intervention. This includes infants with normal results of the postnatal chest radiograph, which may not be sufficiently sensitive to detect a small BPS.

Radiographic appearance

●Chest radiograph – On a chest radiograph, sequestrations typically appear as a uniformly dense mass within the thoracic cavity or pulmonary parenchyma (image 4) [52]. Recurrent infection can lead to the development of cystic areas within the mass [52,53]. Air-fluid levels due to bronchial communication are seen in 26 percent of intralobar sequestrations (ILS) [54].

Most sequestrations occur in the lower lobes. However, they can occur anywhere within the thorax, and extralobar sequestration (ELS) sometimes occurs in a subdiaphragmatic location or as a retroperitoneal mass. The left hemithorax is almost always involved in ELS, and it is usually involved in ILS. (See 'Anatomic characteristics' above.)

●CT – The parenchymal abnormalities associated with BPS are best visualized using CT, although their appearance is variable [54,55]. The most common appearance is a solid mass that may be homogeneous or heterogeneous, sometimes with cystic changes (image 5). Less frequent findings include a large cavitary lesion with an air-fluid level, a collection of many small cystic lesions containing air or fluid, or a well-defined cystic mass. Emphysematous changes at the margin of the lesion are characteristic, although they may not be visible on the chest radiograph.

Conventional CT does not consistently demonstrate the aberrant systemic artery, with visualization in 16 of 24 cases in one series [55]. Lack of visualization was thought to be due to the small size (sometimes as small as 1 mm) or unfavorable orientation of the vessel. These small vessels may be detected by contrast-enhanced or helical CT, which also enables evaluation of abnormalities in the lung parenchyma or airways (image 6) [54,56,57]. Advances in the use of multidetector CT angiography have improved our ability to simultaneously visualize the arterial supply, venous drainage, and parenchymal involvement of pulmonary sequestrations and may make this the diagnostic procedure of choice (image 1A) [58].

●MRI – MRI can demonstrate the location of the lesion and define the aberrant artery and venous drainage, especially if enhanced three-dimensional magnetic resonance angiography (MRA) is used [54,59,60]. However, CT allows sharper delineation of thin-walled cysts and emphysematous changes than MRI [54]. Advanced imaging with either CT and MRI are adequate to evaluate most infants, and the choice between these techniques depends primarily on institutional or clinician preference.

●Ultrasonography – Ultrasonography is not generally necessary in the evaluation of BPS. CT and MRI are superior for identifying the vascular supply, but if these studies are not available, Doppler ultrasound may be helpful to identify the characteristic aberrant systemic artery that arises from the aorta and to delineate venous drainage. In addition, ultrasonography can be used to guide biopsy of a subdiaphragmatic mass [54,55,61,62]. The typical sonographic appearance of BPS is an echogenic homogeneous mass that may be well defined or irregular [54]. However, some lesions have a cystic or more complex appearance.

DIAGNOSIS — Extralobar sequestration (ELS) may be first suspected based on prenatal ultrasonography. Intralobar sequestration (ILS) is more often suspected in an older infant or child who presents with recurrent pulmonary infection. Both types of BPS may be identified as an incidental finding on a plain radiograph in an asymptomatic child. Subsequently, a provisional diagnosis can be made in some cases by advanced imaging (computed tomography [CT] or magnetic resonance imaging [MRI]), if an aberrant systemic artery can be identified with confidence. Advanced imaging may help to distinguish among ILS, ELS, and hybrid lesions but is not completely reliable in making these distinctions. The final definitive diagnosis is only made by pathologic examination after surgical resection. (See 'Anatomic characteristics' above.)

DIFFERENTIAL DIAGNOSIS — The differential diagnosis of BPS includes other cystic lung lesions, such as congenital pulmonary airway malformations (CPAM). In contrast with BPS, CPAMs are connected to the tracheobronchial tree and are supplied from the pulmonary circulation. Hybrid lesions, with features of CPAM and BPS, occur in a substantial proportion of BPS. Advanced imaging (contrast-enhanced computed tomography [CT] or magnetic resonance imaging [MRI]) usually is sufficient to distinguish BPS from these other lesions. (See 'Hybrid BPS/CPAM lesions' above and "Congenital pulmonary airway malformation".)

In addition to CPAM, lesions that may coexist with BPS or mimic BPS on prenatal ultrasound or postnatal plain radiographs include other space-occupying chest lesions, including:

●Congenital diaphragmatic hernia (see "Congenital diaphragmatic hernia: Prenatal issues" and "Congenital diaphragmatic hernia in the neonate")

●Bronchogenic cyst (see "Congenital anomalies of the intrathoracic airways and tracheoesophageal fistula", section on 'Bronchogenic cyst')

●Mediastinal tumors such as a teratoma or neuroblastoma (see "Epidemiology, pathogenesis, and pathology of neuroblastoma")

The radiographic appearances of other congenital abnormalities of the lung are discussed in detail separately. (See "Radiographic appearance of developmental anomalies of the lung".)

MANAGEMENT — The approach to treatment depends upon whether the patient has symptoms (respiratory distress or recurrent infections) or is asymptomatic.

Symptomatic patients — All patients with BPS who are symptomatic should undergo surgical excision, which is curative and is associated with minimal morbidity [31,41,63,64]. Surgery is performed urgently in newborns with significant respiratory distress. It may be done electively in older children who present with recurrent infection, which is usually due to intralobar sequestration (ILS) (algorithm 1). Advanced thoracic imaging (computed tomography [CT] or magnetic resonance imaging [MRI]) should be performed prior to surgery to confirm the diagnosis and assist in surgical planning. (See 'Postnatal imaging' above.)

Complete excision of ILS usually requires lobectomy or segmental resection. Resection of extralobar sequestration (ELS) is simpler because the lesion has its own pleural investment. With both types, all vascular connections to the lesion must be identified and ligated. The arterial supply of these lesions may arise from the subdiaphragmatic aorta, and careful identification of the feeding vessel is crucial. Thoracoscopic lobectomy is an alternative to thoracotomy in infants and older children with ILS or ELS [65-67]. For lesions with a single, well-characterized systemic arterial supply and where high-output cardiac failure is a concern, treatment by arterial embolization may be an effective option for initial therapy. Case series describe treatment using a variety of embolization techniques [68-73]. Lesions with multiple feeding arteries may require repeated procedures, making embolization less appealing.

Asymptomatic patients — Infants with suspected BPS who are asymptomatic at birth should be closely observed for the first few days of life as some may develop symptoms in the immediate postnatal period [74]. For infants and children who remain completely asymptomatic, the decision between surgical management and observation is controversial [75,76]. Management decisions for these patients are similar to those for asymptomatic patients with other congenital abnormalities of the lower airways, the most common of which are congenital pulmonary airway malformations (CPAM).

Our approach to asymptomatic patients with BPS depends on the results of the imaging work-up, as outlined in the algorithm (algorithm 1). This algorithm applies to all congenital abnormalities of the lower airway identified on prenatal ultrasound, among which BPS will be a minority.

High risk — We suggest early surgical resection for patients with any of the following characteristics, which suggest increased risk for developing complications:

●Large lesion (occupies ≥20 percent of the hemithorax)

●Characteristics suggesting risk for pleuropulmonary blastoma (bilateral or multifocal cysts, pneumothorax, or a family history of pleuropulmonary blastoma-associated conditions (table 1))

Low risk — For asymptomatic patients with none of the above characteristics on advanced imaging, either elective surgical resection or observation is a reasonable option (algorithm 1). The decision is influenced by the family's preferences after a detailed discussion of the potential benefits and risks of each approach.

●Elective surgical resection – In our practice, we generally perform surgery for asymptomatic infants with BPS, even those considered at low risk for developing complications of BPS. We generally perform this elective surgery between 6 and 12 months of age. Surgery may not be appropriate for some infants who have increased surgical risks due to coexisting congenital anomalies.

Our rationale for surgery is threefold: First, surgery is curative and not generally associated with significant complications [75,77]. Second, individuals with BPS appear to have a moderate risk for developing infection sometime later in life, particularly if the lesion is an ILS [4,17,74]. When infection or respiratory symptoms do develop, surgery becomes urgent and is associated with an increased risk of postoperative complications (eg, air leak, effusion, or pneumonia) compared with elective surgery performed in asymptomatic patients (17 versus 5 percent in one of these reports [78]). Third, imaging is not always able to distinguish between BPS and CPAM or hybrid lesions, and CPAM or hybrid lesions are associated with a risk of developing complications (infection or malignant degeneration) if they are left in place. A secondary consideration is that early surgery may have advantages for compensatory lung growth, although pulmonary function outcomes are generally good for either early or later surgery. (See "Congenital pulmonary airway malformation", section on 'Asymptomatic patients'.)

●Observation – Some authors recommend observation rather than surgery for asymptomatic patients, particularly if the lesion is small, noncystic, and appears to be consistent with ELS [76,79]. If observation is chosen, both chest radiographs and advanced thoracic imaging (CT or MRI) have been recommended for monitoring of these patients, though there is no consensus on the optimal strategy for imaging [80,81].

Thus, the optimal management for asymptomatic low-risk infants remains unclear because of limited information about the natural history of BPS and difficulty establishing a definitive diagnosis by imaging. Indeed, most case series include infants with either BPS or CPAM and report outcomes without distinguishing between the conditions. For asymptomatic infants managed conservatively (without surgery), the incidence of complications varies widely in different reports, ranging from 3 to 86 percent [76,78,82,83]. The complications are primarily infection or respiratory symptoms, typically occur between 7 and 24 months of age, and require surgery. These analyses do not report specifically on the risks for complications associated with BPS versus CPAM, or for ELS versus ILS, but small case series suggest that complications are particularly common in individuals with ILS [33].

OUTCOME — In the absence of other significant congenital anomalies, the prognosis for children with BPS is generally very good [6,77,80,81,84,85]. Most case series do not distinguish outcomes for BPS from those for other congenital abnormalities of the lower airway, particularly congenital pulmonary airway malformations (CPAM).

For asymptomatic infants with CPAM or BPS who were managed conservatively (without surgery), the outcome is not well established, since the incidence of complications (such as infection) varies widely in different reports, as discussed above (see 'Low risk' above). Furthermore, most of the available data come from series in which most infants had CPAM rather than BPS.

For symptomatic infants who undergo emergency surgery, at least 20 percent have postoperative complications, which include air leak, infection, or effusion [78]. For asymptomatic infants who undergo elective surgery, approximately 10 percent have postoperative complications.

Long-term pulmonary outcomes for both of these groups are generally good and appear to depend upon the extent of the lung resection. The remaining lung parenchyma undergoes compensatory growth and development [85]. These outcomes vary across different reports, probably reflecting differences in patient selection (eg, asymptomatic lesions identified on prenatal ultrasound and managed conservatively or with elective surgery versus symptomatic lesions requiring surgery during infancy). (See "Congenital pulmonary airway malformation", section on 'Outcome'.)

SUMMARY AND RECOMMENDATIONS

●Definition and types – Bronchopulmonary sequestration (BPS) is a rare congenital abnormality of the lower respiratory tract. It consists of a nonfunctioning mass of lung tissue that lacks normal communication with the tracheobronchial tree and receives its arterial blood supply from the systemic circulation. The connections to the tracheobronchial tree and systemic artery distinguishes BPS from congenital pulmonary airway malformation (CPAM). (See 'Anatomic characteristics' above.)

•An intralobar sequestration (ILS) is located within a normal lobe and lacks its own visceral pleura. This type often has aberrant connections to bronchi, lung parenchyma, or the gastrointestinal tract and often presents with recurrent infections.

•An extralobar sequestration (ELS) is located outside the normal lung and has its own visceral pleura. Infectious complications are rare, except in ELS with connections to the gastrointestinal tract or intrapulmonary structures, which is unusual.

●Associated anomalies – Congenital abnormalities that are sometimes associated with BPS include congenital diaphragmatic hernia, vertebral anomalies, congenital heart disease, pulmonary hypoplasia, colonic duplication, and CPAM. These associated anomalies are more common in ELS compared with ILS. (See 'Associated anomalies' above.)

●Clinical presentation – The clinical presentation of BPS is variable and depends on the type, size, and location of the lesion. Many cases are initially detected by prenatal ultrasound; most of these regress during gestation, while others progress and hydrops may develop. The affected newborn is usually asymptomatic but sometimes presents with respiratory distress. Some cases (usually ILS) present with recurrent pneumonia during infancy or childhood. (See 'Clinical presentation' above.)

●Postnatal evaluation – All cases of BPS or other congenital abnormalities of the lower airway should be further evaluated with postnatal imaging. This includes cases that regressed or appeared to resolve in utero because few lesions resolve completely and advanced imaging is more sensitive than prenatal ultrasound for detecting small lesions. (See 'Postnatal imaging' above.)

•After birth, the first step is a plain chest radiograph. On a chest radiograph, sequestrations typically appear as a uniformly dense mass within the thoracic cavity or pulmonary parenchyma (image 4). Recurrent infection can lead to cystic areas within the mass, and there may be air-fluid levels if the lesion communicates with a bronchus.

•The second step is advanced thoracic imaging, the timing of which depends on the patient's characteristics, as outlined in the algorithm (algorithm 1). This is to confirm the diagnosis, including identifying the aberrant artery that distinguishes BPS, and to help with surgical planning.

●Management

•Symptomatic – Infants with BPS that is causing any respiratory symptoms (respiratory distress or tachypnea) are treated with surgical excision; surgery is curative and is associated with minimal morbidity. The procedure is performed urgently in newborns with significant respiratory distress. Surgical resection is typically performed electively in older children who present with infection. (See 'Symptomatic patients' above.)

•Asymptomatic, high risk – For asymptomatic patients of any age with characteristics that suggest a high risk for developing complications (large lesions occupying >20 percent of the hemithorax, bilateral or multifocal cysts, pneumothorax, or a family history of pleuropulmonary blastoma-associated conditions (table 1)), we suggest surgical resection rather than observation (Grade 2C). (See 'High risk' above.)

•Asymptomatic, low risk – For asymptomatic patients without these high-risk characteristics, either elective surgical resection or conservative management with observation are reasonable options and practice varies (algorithm 1). (See 'Low risk' above.)

-In our practice, we generally perform surgery for all asymptomatic infants with BPS, regardless of the lesion's size and characteristics. The surgery is elective and is usually performed between 6 and 12 months of age. Our preference for surgery is based on the good outcomes after surgery and on the risk of developing complications (primarily infection) if surgery is not performed. The likelihood and risk factors for developing complications if surgery is not performed are poorly delineated. (See 'Outcome' above.)

-Other authors prefer to observe asymptomatic patients, especially if the lesion is small, noncystic, and appears to be consistent with ELS. Optimal surveillance strategies for observation have not been determined.