Congenital Diaphragmatic Hernia

Congenital diaphragmatic hernia (CDH) results from a developmental defect during the formation of the diaphragm that allows for the herniation of abdominal contents into the thoracic cavity (see Chapter 78). Defects of the diaphragm are classified according to the anatomic region of the diaphragm that is defective. The most common defect involves the posterolateral diaphragm (Bochdalek) and accounts for 70% of diaphragmatic hernias. Anterior diaphragm defects (Morgagni) account for 25% to 30% of diaphragmatic hernias, and central diaphragmatic defects are rare, occurring in 2% to 5%.⁶⁰ The incidence of CDH is 1 in 2000 to 3000 newborns, and it occurs most commonly on the left side (85%), whereas bilateral hernias are rare (1%) and usually fatal.

Congenital diaphragmatic hernia is either an isolated defect or can be associated with other congenital anomalies, including cardiac, urogenital, chromosomal, and musculoskeletal. Most reports estimate that 40% to 60% of patients with CDH have non–hernia-related anomalies.¹¹⁸ In a review of 3062 patients with CDH, the Congenital Diaphragmatic Hernia Study Group reported a 28% incidence of severe malformations (major cardiac, syndromal, and chromosomal disorders) in patients who did not undergo surgical repair secondary to unsalvageable hernia compared with 7% in repaired patients.²⁵ This emphasizes the importance of adequate evaluation of associated malformations in patients with CDH.

The underlying pathophysiology of CDH is that of pulmonary insufficiency and persistent pulmonary hypertension of the newborn (PPHN) secondary to pulmonary hypoplasia, lower number of alveoli, and airway and vascular muscular hypertrophy associated with compression by abdominal contents. Pulmonary hypoplasia may also have a primary developmental component, as animal models have confirmed that developmental regulation of the lung and diaphragm are controlled by some of the same genes. The severity of CDH is related mostly to the degree of lung hypoplasia, which depends on the size of the defect, the presence of the liver in the chest, and how early in gestation the abdominal contents were displaced.²⁵

In a review of reports from 13 tertiary centers, 56% of CDH cases were diagnosed antenatally. Antenatal diagnosis is associated with a poor prognosis, and the data suggest that infants with a prenatal diagnosis have a better chance of survival if they are born in a tertiary center.⁷⁵ Several antenatal parameters have been evaluated for their ability to predict survival and morbidity in cases of isolated CDH. Most of these predictors rely on the indirect assessment of the size of the contralateral lung as a proxy for pulmonary hypoplasia. Methods used include lung area to head circumference ratio (LHR) between 22 and 28 weeks’ gestation, the presence of the liver in the chest (which has been thought to be most predictive), and estimated fetal lung volume by MRI.^{20,50,54,56,79} Because it has been reported that the LHR increases exponentially with gestational age, some experts have advocated that the LHR should be corrected for gestational age and have used an observed : expected LHR (O/E LHR) based on the LHR in the CDH patient compared with what is considered normal for that gestational age.⁵⁵ When using the corrected LHR, the CDH registry has quoted the following numbers based on 184 fetuses with isolated left-sided CDH evaluated between 22 and 28 weeks’ gestation:³⁷

The clinical presentation of patients with CDH can vary from asymptomatic in mild cases to severe respiratory failure at birth. Diagnosis should be suspected in previously undiagnosed patients by the presence of severe respiratory distress, cyanosis, scaphoid abdomen, and failure to improve with ventilation. Physical examination reveals absence of breath sounds on the affected side with displacement of heart sounds to the contralateral side, and occasionally bowel sounds can be heard over the thorax. Once the diagnosis is made or suspected, patients should be immediately intubated and an orogastric tube placed to evacuate the stomach. Aggressive ventilatory strategies should be avoided (see later). Chest radiograph shows the presence of bowel loops in the affected chest cavity with shifting of the heart to the contralateral side (Figure 74-2). If the stomach is included in the hernia, the tip of orogastric tube will be seen within the thorax. The presence of liver in the chest is suspected by deviation of the umbilical venous line. Late presentation of Bochdalek hernia occurs in less than 3% of cases.⁶⁴ These patients can be asymptomatic at birth and usually present later in life with respiratory or gastrointestinal symptoms. High index of suspicion is needed in these cases to prevent unwarranted and potentially dangerous interventions such as the insertion of a chest tube for suspected pleural effusion or pneumothorax. Diagnosis can be made after nasogastric tube insertion, contrast upper gastrointestinal study, or chest computed tomography (CT) scan. Prognosis for cases with late presentation is excellent once the correct diagnosis is made.

Improved survival has been reported using a consistent approach in the management of CDH that can be facilitated by the development of multidisciplinary standardized treatment guidelines, including input from neonatology, pediatric surgery, extracorporeal membrane oxygenation (ECMO) specialists, and respiratory therapy (Box 74-2). Predetermined criteria for the use of ECMO and an underlying “protect the lung” strategy are essential components in the care of these infants and can be as important as the specific medical interventions chosen. Whereas animal studies have suggested lung immaturity and surfactant deficiency in models of CDH, the use of antenatal steroids and surfactant replacement has not been shown to be beneficial.¹¹² A systematic review of strategies associated with improved survival among infants with CDH in 13 centers that cared for at least 20 patients and reported a survival rate of 75% or more has described multiple successful treatment strategies associated with this improved survival.⁷⁵ Although these centers used different mechanical ventilation strategies, most of these targeted the use of gentle ventilation or permissive hypercapnia. The basic elements of this treatment strategy are:

Postnatal survival rate at tertiary centers has improved with reported rates of 70% to 92%.38,45,46,59,77,83 However, the survival data might underestimate hidden mortality secondary to termination, stillborn, and referral pattern for outborn patients. With improvement in survival, there has been a focus on improving long-term morbidity of survivors. Infants born with CDH have multiple long-term morbidities affecting the pulmonary, gastrointestinal, neurologic, and skeletal systems. Respiratory complications include pulmonary vascular abnormalities presumably causing pulmonary hypertension, a higher incidence of obstructive airway disease, and a restrictive lung function pattern that continues into adulthood.¹⁰⁰ Gastroesophageal reflux disease (GERD), sometimes in combination with failure to thrive, is a well-recognized complication in patients with CDH, and several patients require antireflux surgery. It is unknown whether GERD has an effect on pulmonary function in this population. Pulmonary hypoplasia and PPHN predispose children born with CDH to a high risk for hypoxemia, which may result in neurodevelopmental delay. It has been reported that infants with CDH are at higher risk to have neuromotor delay, hypotonia, and delayed language skills.²⁴ There is also a high percentage of these infants with sensorineural hearing loss.³³ Chest wall deformities and scoliosis are more common among CDH patients, although deformities are mild and surgery is rarely required.⁸⁴ These data emphasize the need for a multidisciplinary team approach in the postoperative management and follow-up of all survivors of CDH. The AAP section on surgery has provided a suggested schedule for follow-up for these children.⁹⁵

Capillary Alveolar Dysplasia

Capillary alveolar dysplasia (CAD) is a rare, often fatal pulmonary disease that presents in the newborn period, usually within the first 48 hours of life with severe hypoxemia and PPHN unresponsive to treatment.¹⁵ The true incidence of the disease is unknown because the diagnosis is made by pathology, and if there is no autopsy or antemortem lung biopsy, the diagnosis cannot be made; thus, what is reported in the literature likely underestimates the true incidence of the disease. Histologically, CAD is characterized by paucity of capillaries proximal to the alveolar epithelium, anomalous distended pulmonary veins within the bronchovascular bundle rather than within the interlobular septae, and immature alveolar development with medial thickening of small pulmonary arteries and muscularization of the arterioles, and in approximately one third of cases, lymphangiectasis. These characteristic findings are diffuse in 85% of patients and patchy in the remainder. Although the mechanisms underlying the pathogenesis of CAD and its associated pulmonary hypertension are not fully understood, it has been suggested that it is related to a failure of fetal lung vascularization with capillary hypoplasia and discontinuity of these capillaries and pulmonary veins impairing pulmonary blood flow, as well as a component of reactive pulmonary vasoconstriction mediated by hypoxia.^31,99 Extrapulmonary findings are present in 50% to 80% of cases, most commonly affecting the gastrointestinal, genitourinary, and cardiovascular systems.^11,96 Although the disease is mostly sporadic, reports of multiple affected siblings in subsets of families suggest an autosomal recessive inheritance pattern. Mutations of the FOXF1 gene located on chromosome 16q24.1 have been identified in 40% of a large cohort of patients with CAD. This may allow for prenatal genetic testing of high-risk families; however, it will not identify all cases of CAD.¹⁰¹

Most patients with CAD present within the first few hours of life. These infants are usually born at term and have appropriate size and normal Apgar scores. Although these babies might be asymptomatic at delivery, respiratory distress, cyanosis, and hypoxemia progress quickly to respiratory failure in more than half of these patients within hours after delivery. About 14% of these patients do not present with symptoms until 2 to 6 weeks of life. Treatment is always unsatisfactory. Although a transient response to iNO might be observed, PPHN is not responsive to medical treatment, and the disease progression is that of a fulminant course and rapid progression to death, although there are reports of survival beyond the neonatal period. High index of suspicion and diagnostic lung biopsy are required to avoid the use of more invasive and futile treatments, including ECMO.

Congenital Pulmonary Lymphangiectasia

Congenital pulmonary lymphangiectasia (CPL) is a pulmonary disorder first described by Virchow in 1856, but to date there are very few cases reported in the literature. Most cases of CPL are sporadic with a predilection for male involvement (2 : 1). However, familial presentations have been described, suggesting an autosomal recessive inheritance pattern. Congenital pulmonary lymphangiectasia is classified as primary or secondary. Primary CPL can present as either a primary pulmonary developmental defect that can be localized or diffuse, or as a part of a more generalized lymphatic developmental defect. Patients with generalized lymphangiectasia tend to have less severe pulmonary involvement. Secondary cases of CPL are often associated with cardiac malformations with obstructed pulmonary venous return, including obstructed total anomalous pulmonary venous return, hypoplastic left heart syndrome, and cor triatriatum. Congenital pulmonary lymphangiectasia has also been described in multiple syndromes, including Noonan, Down, and Ullrich-Turner. The characteristic pathologic finding of CPL is pulmonary lymphatic dilation in the subpleural, interlobar, perivascular, and peribronchial lymphatics. It may be associated with non–immune hydrops fetalis and congenital chylothorax.¹⁴

The etiology of CPL is not clear but is thought to be secondary to a failure of regression of lymphatics that normally occurs between 16 and 20 weeks’ gestation. Multiple genes have been found to be involved in lymphatic development, including FOXC2,¹¹⁰ vascular endothelial growth factor 3,¹⁰² and integrin a9b1 genes. Mice homozygous for a null mutation in the integrin a9 subunit gene died of respiratory failure caused by bilateral chylothorax within 6 to 12 days after birth with pathologic features similar to those in CPL.⁵²

Patients with CPL usually present with intractable respiratory failure, cyanosis, and hypoxia associated with bilateral chylothoraces in the first few hours of life, although diagnosis can be delayed for several weeks in cases of unilobar involvement. Nonimmune hydrops is also a well-recognized presentation in patients with CPL. Examination of the pleural fluid shows characteristic findings of chylothorax, including a lymphocytosis and elevated triglycerides, although elevated triglycerides might be absent in non-fed infants (see later). Chest radiograph reveals hyperinflation of the lung with bilateral interstitial infiltrates and bilateral pleural effusions. High-resolution computed tomography demonstrates diffuse thickening of the peribronchovascular interstitium and the septa surrounding the lobules. Definitive diagnosis is made by lung biopsy showing the characteristic features, although differentiation from lymphangiomatosis can be difficult.¹⁴

Treatment is mostly supportive. Intubation and mechanical ventilation, drainage of pleural and peritoneal effusions, and correction of hypoxia, acidosis, and shock might be needed in the delivery room for stabilization. Persistent chylothorax might require chest tube placement. Nutritional therapy with medium-chain triglycerides and total parenteral nutrition has been successful in the treatment of CPL. Case reports of using octreotide and antiplasmin to treat CPL as well as intestinal lymphangiectasia have been reported with success.¹⁴ Pleurodesis with sclerosing agents has been used to treat persistent chylothoraces associated with the disease. The prognosis appears to depend on the severity of symptoms in the immediate newborn period. Although traditionally thought to be fatal, there are reports of survival in some patients presenting with respiratory failure, chylothorax, and hydrops fetalis in the immediate neonatal period. Later presentation carries a better prognosis with the possibility of spontaneous resolution, although respiratory morbidity might be common.

Chylothorax

Chylothorax is the accumulation of lymphatic fluid (chyle) in the pleural cavity and is the most common cause of pleural effusion in neonates and can be primary (congenital) or secondary (acquired). It is a rare entity, with a reported incidence of 1 : 10,000 births, and affects males more than females (2 : 1).⁴⁰ Congenital chylothorax, which accounts for less than 10% of all chylothoraces, may be associated with abnormalities of the lymphatic system, congenital malformations such as congenital heart disease or mediastinal malignancies, or chromosomal abnormalities such as trisomy 21, Noonan syndrome, or Turner syndrome. Secondary chylothoraces are most commonly associated with trauma during thoracic surgery, but can also be the result of increased superior vena caval pressure caused by venous thrombosis.

Clinical presentation is that of respiratory distress secondary to lung compression, pulmonary hypoplasia, or symptoms of the underlying pulmonary or cardiac disease. Many cases of congenital chylothorax are diagnosed by prenatal ultrasound, and antenatal management consists of thoracocentesis or thoracoamniotic shunt placement to try to prevent the development of pulmonary hypoplasia. However, even with prenatal treatment, these infants can still present with significant respiratory distress at birth as fluid reaccumulates, requiring postnatal treatment.

Physical examination is significant for decreased breath sounds on the affected side with shifting of the cardiac apex to the contralateral side. Chest radiograph shows a pleural effusion, compression of the lung on the affected side, and displacement of the heart to the opposite side. Diagnosis is established by analysis of the pleural fluid. In neonates with established feedings, chylothorax appears milky in color; however, in non-fed neonates, it is clear. Buttiker and colleagues have proposed the following criteria for establishing the diagnosis of chylothorax: absolute cell count of greater than 1000/µL with a lymphocyte fraction of greater than 80% and triglyceride levels greater than 1.1 mmol/L.¹⁹

Optimal treatment for chylothoraces has not been defined, but is mostly supportive while awaiting resolution of the effusion. Mechanical ventilation and drainage of the chylothorax might be needed in patients with large effusions, and nutritional support using total parenteral nutrition is essential. When feedings are started, formulas containing a high percentage of medium-chain triglycerides (MCTs) are recommended because lymphatics are not needed for MCT absorption. In most cases, spontaneous resolution occurs within 4 to 6 weeks. Several treatment strategies have been described for cases with persistent chylothorax, including pleurodesis, ligation of the thoracic duct, and pleuroperitoneal shunt.¹⁰ Whereas povidone-iodine pleurodesis has been used successfully in persistent chylothorax, it has also been associated with renal failure. There is growing evidence from uncontrolled case studies suggesting a markedly positive effect of somatostatins, particularly octreotide, in the treatment of chylothorax with minimal side effects. In the absence of a controlled trial evaluating safety and efficacy, this therapy should be reserved for persistent and severe cases and not as first line of treatment.^92,98

Congenital Cystic Pulmonary Malformations

Congenital cystic lung disease encompasses a broad spectrum of rare but clinically significant developmental abnormalities, which include congenital cystic adenomatoid malformation (CCAM), more recently referred to as congenital pulmonary airway malformation (CPAM), bronchopulmonary sequestration (BPS), bronchogenic cyst (BC), and congenital lobar emphysema (CLE). These lesions were originally thought to be separate entities; however, the description of coexistence of multiple lesions (bronchogenic cyst, CCAM, and extralobar BPS) in the same patient as well as reports of bronchial atresia in some specimens of all four entities suggests a common embryologic origin. These lesions can be identified on prenatal ultrasound, but the classification of the lesion should wait until postnatal examination and histology are available. These lesions should be followed closely in utero as some of these lesions can predispose the fetus to develop hydrops, and when this occurs in the second trimester, fetal intervention is warranted. Intervention includes repeated cyst aspiration, thoracoamniotic shunting, sclerotherapy, fetal surgery, or more recently, maternal betamethasone treatment. However, fetal intervention is relatively rarely needed as many of these cystic lung lesions appear to regress in utero.

Congenital Cystic Adenomatoid Malformation

Congenital cystic adenomatoid malformation constitutes multiple different hamartomatous lesions arising from the abnormal branching of the immature bronchial tree. This entity was first described by Chin and Tang in 1949,²³ and since then, the term has been evolving as our understanding of the entity improves. For the past 30 years, Stocker has classified the lesions into three types: I, II, and III.¹⁰⁶ Stocker has since described two new types, 0 and 4, and has revised his original term, and now refers to this entity of cystic lung lesions as congenital pulmonary airway malformations (CPAM) to reflect the site of suspected development of the malformation in the tracheobronchial tree and that only three types (1, 2, and 3) are adenomatoid, and only types 1, 2, and 4 are cystic.¹⁰⁵ However, most of the literature still uses the term CCAM and classifies the lesions as types 0 to 4; thus this is how they are referred to in this textbook.

Congenital cystic adenomatoid malformation is the most common congenital cystic lung disease, occurring in 1 in 11,000 to 30,000 live births, and affecting more males.⁹⁷ Both lungs are affected equally, and the disease is most commonly unilobar with predilection for the lower lung lobes. Unlike BPS, it is connected with the tracheobronchial tree and has a pulmonary blood supply (Table 74-1). Congenital cystic adenomatoid malformation develops during the pseudoglandular phase (7 to 17 weeks’ gestation) of fetal lung development. In addition to the classification system described in the preceding, some have suggested classifying the lesions, at least during the prenatal period, as microcystic versus macrocystic based on the gross anatomy and antenatal ultrasound appearance. Whereas the latter classification has poor correlation with histologic features, it has a much better prognostic value, with microcystic lesions (cysts <5 mm) having a poorer prognosis than macrocystic lesions (>5 mm).⁵

TABLE 74-1

Characteristics of Congenital Cystic Adenomatoid Malformation Versus Bronchopulmonary Sequestration

	Congenital Cystic Adenomatoid Malformation	Bronchopulmonary Sequestration
Classification	Types 0-4, microcystic and macrocystic	Intralobar and extralobar
Connection to tracheobronchial tree	Yes	No
Systemic blood supply	No	Yes
Associated malformation	Common	Less common
Location	Either lower lobe	Left lower lobe
Malignant transformation	Yes	Yes
Spontaneous regression of antenatally diagnosed cases	15%	75%

Type 0 CCAM is the rarest form and arises from the trachea or bronchus and contains multiple small cysts. These infants also have other associated lesions, including cardiovascular anomalies, renal hypoplasia, and focal dermal hypoplasia. The lung itself is hypoplastic, weighing only 30% to 50% of the expected weight. Microscopically, the tissue consists almost entirely of irregular bronchial-like structures lined by pseudostratified ciliated columnar epithelium surrounded by thick cartilage plates and bundles of smooth muscle fibers. Usually all lobes of the lung are involved; thus this diagnosis is usually lethal.¹⁰⁵

Type 1 CCAM is the most common form, representing 60% to 70% of all CCAMs.¹⁰⁴ These lesions consist of large cysts (1-10 cm) surrounded by multiple small cysts that arise from the distal bronchus or proximal bronchiole and are rarely associated with other congenital malformations. These CCAMs can be large and can have significant mass effect in utero, which can lead to fetal hydrops and pulmonary hypoplasia. However, many of these cysts collapse as pregnancy progresses, allowing normal lung growth of the unaffected lobes. Radiographically, they appear as either a single or multiple air-filled or air/fluid-filled cysts in one or (much less frequently) multiple lobes. Depending on size, there can be flattening of the diaphragm, mediastinal shift and compression of adjacent lung. Overall, these lesions have a good prognosis. However, a number of reports describe the occurrence of a bronchioloalveolar carcinoma, especially when the CCAM is not fully resected, with a malignant transformation risk of 1%.¹¹⁵

Type 2 CCAM accounts for 15% of all CCAMs and is the second most frequent type of CCAM. These malformations are of bronchiolar origin and consist of multiple small cysts (0.5-2 cm) and are often (≈50%) associated with other congenital anomalies, including renal agenesis/dysplasia, cardiovascular anomalies, congenital diaphragmatic hernia, and extralobar sequestrations.26,105 Radiographically, they are characterized by multiple small cysts that may not even be visible on chest x-ray. Prognosis is usually related to the severity of the associated anomalies.

Type 3 CCAM accounts for 5% to 10% of all CCAMs. These are of bronchiolar/alveolar duct origin and almost exclusively seen in males. These lesions were the original congenital adenomatoid malformation described by Chin and Tang in 1949.²³ They consist of multiple smaller cysts (rarely >0.2 cm) and appear as a solid mass that is associated with a significant risk of hydrops and polyhydramnios resulting from caval obstruction and cardiac compression secondary to mediastinal shift. This also leads to pulmonary hypoplasia, because unlike type 1 CCAMs, this lesion does not regress with progression of pregnancy. The extent of the pulmonary hypoplasia is the primary determinant of survival.

Finally, type 4 CCAM accounts for approximately 10% of CCAMs, and is of distal acinar origin. The lesion primarily consists of large (up to 10 cm) air-filled, thin-walled cysts usually located at the lung periphery. This lesion can be asymptomatic at birth, and presents from the neonatal period to 4 years of age. Often, this will be an incidental finding on an x-ray that was taken for other reasons, such as acute respiratory distress related to a tension pneumothorax, or pneumonia. This lesion can be confused with pleuropulmonary blastema; therefore, blastemas must be looked for histologically. Surgical resection of the lobe is accompanied by an excellent prognosis.¹⁰⁵

With improvement in prenatal imaging, most of these lesions are diagnosed prenatally, but some may not present until the postnatal period either as acute respiratory distress or as an incidental finding on a chest x-ray that was obtained for other reasons. Although the diagnosis of a congenital lung lesion is able to be made on prenatal ultrasound, it is difficult to distinguish CCAM from other cystic lung lesions. Adzick et al. proposed the classification of antenatal cystic lung lesions based on their appearance on ultrasound as either macrocystic (cysts ≥5 mm) or microcystic (cysts <5 mm).⁵

Our understanding of the natural history of CCAMs continues to evolve. Up to 15% of these lesions appear to “disappear” in the prenatal period, usually after 28 weeks’ gestation when the growth of these lesions tends to plateau; however, in most all cases, postnatal CT scan or fetal MRI will show persistence of the anomaly (Figure 74-3). The unpredictability of the in utero growth of these lesions requires careful follow-up. Midgestation, these lesions can grow quite rapidly, which can cause mediastinal shift, pulmonary hypoplasia, and impaired venous return leading to hydrops. It has been well established that the diagnosis of fetal hydrops associated with CCAM portends a poor prognosis, with mortality near 100%.^3,4,114 In 2002, it was hypothesized that the volume of the lesion would predict whether hydrops would develop in the fetus. The CCAM volume ratio (CVR) was developed as a prognostic tool and is calculated by measuring the three dimensions of the lung lesion and dividing by the head circumference. A CVR greater than or equal to 1.6 at initial diagnosis was found to reliably predict a subgroup of fetuses at increased risk for developing fetal hydrops, and is now used to evaluate which infants might benefit from in utero interventions.³⁰ Fetal surgery using thoracoamniotic shunting or cyst aspiration has been successful for macrocystic lesions, with survival rates in hydropic fetuses of 50% and 69%, respectively.²² Microcystic lesions require open fetal surgery in the presence of hydrops with a survival rate of 52%^2,30,48,114 (see Chapter 14). Patients who are not suitable for surgery might benefit from antenatal steroids, which have been shown to decrease the size of microcystic CCAMs as well as resolve the hydrops in several case series.⁸⁷ The EXIT procedure should be considered in patients with significant mediastinal shift and cardiac and lung compression at time of delivery.^12,62

Postnatally, all CCAMs should have surgical evaluation. If the infant is symptomatic, surgical excision is indicated. However, there is still some debate over the appropriate management of those lesions that are asymptomatic at birth. All infants with CCAM should have a chest x-ray in the immediate neonatal period and chest CT scan at 4 to 6 weeks of age to evaluate the mass. There are justifications for prophylactic surgery: preventing chest infections and sepsis; preventing malignancy; early rather than delayed surgery may encourage compensatory lung growth; reduction in postoperative complications (compared with emergency surgery).⁶⁵ The majority opinion seems to favor elective resection at 2 to 6 months of age. Following successful resection, the long-term functional outcome of children with CCAM is excellent with no physical limitations or increased risk for infection, although RSV immunoglobulin prophylaxis is advised in these patients.¹²

Bronchopulmonary Sequestration

Bronchopulmonary sequestrations (BPSs) are microscopic cystic masses of nonfunctioning lung tissue thought to arise from the primitive foregut. Usually, these structures are not connected to the main airway, and their blood supply arises from the systemic circulation. Two forms are recognized: intralobar sequestration (ILS) and extralobar sequestration (ELS). Intralobar sequestration occurs when the accessory bud arises before the establishment of the pleura and is contained within the normal lung. If the accessory lung bud arises after the pleura are established, it has its own pleural covering and is completely separated from the normal lung and is classified as an ELS. Extralobar sequestrations are usually located supradiaphragmatic; however, a small portion (<10%) are located infradiaphragmatic.43,69 This is dependent on the level of the foregut at which they arise.

On antenatal ultrasound, sequestrations appear as well-defined, solid, echogenic masses very similar to type 3 CCAM. A distinguishing feature of BPS is the documentation of systemic blood supply by color Doppler. If unclear, ultrafast MRI can establish the blood supply, define the lesion, and identify other associated malformations. It is difficult to distinguish ELS from ILS on prenatal ultrasound unless it is surrounded by a pleural effusion or is located below the diaphragm, which can only be features of an extralobar sequestration. Intra-abdominal ELS appears as a suprarenal solid mass and should be differentiated from other suprarenal masses, including neuroblastoma and mesoblastic nephroma.⁹⁷ Antenatal or postnatal echocardiography can show associated cardiac malformation. Bronchopulmonary sequestration appears on chest radiograph as a posterior thoracic mass mostly on the left. Chest CT scan or even MRI might be needed to further delineate systemic blood supply.

Like CCAMs, sequestrations, extralobar more so than intralobar, can be associated with multiple congenital malformations, including congenital diaphragmatic hernia, congenital heart disease, and vertebral anomalies. A feature unique to BPS is high output cardiac failure owing to the sequestration’s redundant circulation and occasionally massive left-to-left shunt. Like a CCAM, BPS can also cause fetal hydrops, either from the mass effect or from a tension hydrothorax that is the result of either fluid or lymph secretion from the BPS or from high output cardiac failure. If there is significant in utero compromise of the fetus, fetal intervention may be necessary in the form of a thoracoamniotic shunt for decompression of pleural effusion, surgical excision, or EXIT procedure.2,28,35

The natural history of BPS is still being learned. Most BPSs (68%) dramatically decrease in size as pregnancy progresses.² Thus most sequestrations are usually asymptomatic in the neonatal period. If the sequestration is large, it can act as a space-occupying lesion and present as respiratory insufficiency either from pulmonary hypoplasia or lung compression and may require emergent surgical repair. If asymptomatic in the neonatal period, sequestrations can present later with recurrent pneumonia, atelectasis, bleeding, or high-output congestive heart failure. It is felt that asymptomatic patients should undergo elective resection to prevent complications of malignancy or infection.²⁸

While discussing CCAMs and BPSs, it should be noted that there are some lesions, called hybrid lesions, that exhibit features of both entities.43,69

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