Congenital lung malformations considered in this article are those occurring in the lung below the carina. Airway, pleural-space, and chest-wall malformations are considered elsewhere. Some of these topics are covered in greater detail in other Medscape Reference articles (see Laryngomalacia, Pediatric Tracheomalacia, Pediatric Pulmonary Hypoplasia, Cystic Adenomatoid Malformation, and Pediatric Bronchogenic Cyst).
The aim here is to provide a concise approach to congenital lung malformations. Therefore, this article discusses bronchogenic cyst, pulmonary agenesis and hypoplasia, polyalveolar lobe, alveolocapillary dysplasia, sequestration including arteriovenous malformation (AVM) and scimitar syndrome, pulmonary lymphangiectasis, congenital lobar emphysema (CLE), and cystic adenomatoid malformation (CAM) and other lung cysts.
Although they secrete the amniotic fluid, the lungs are unnecessary as organs of respiration in fetal life. However, their development must occur so that air exchange may take place at birth. The lungs go through embryonic, pseudoglandular, canalicular, saccular, and alveolar phases.
The early division and growth of the lung bud is directed by the epithelial-mesenchymal interaction. Thus, asymmetry of lung buds (3 main bronchi on the right, 2 on the left) is apparent in the embryonic phase. At this time the pulmonary vessels form, arising from the sixth pharyngeal arch.
The 16 generations of the conducting division are laid down in the pseudoglandular phase (8-16 weeks' gestation), which is characterized by cubic epithelium surrounded by mesenchyma. The lung looks like a gland. Bombesin-related gastrin-releasing peptide plays an important role in lung growth, response to injury, and tumorigenesis. Type II pneumocytes (the alveolar cells) appear.
In the next phase (16-24 weeks' gestation), canaliculi with a wider lumen, more capillaries, and flatter epithelial cells branch out of the terminal bronchioles and form the respiratory parenchyma. The type II pneumocytes begin to produce the surfactant and the ratio of lecithin to sphingomyelin increases in the amniotic fluid.
The final, seventh generation of air spaces in the respiratory division develop at the end of the saccular phase (24-36 weeks' gestation). Thus, 16 generations of airways are noted in the conducting division, and 7 generations are noted in the respiratory division.
Large number of alveoli then bud from the airspaces in the alveolar phase, which continues in the postnatal life. Epimorphin/syntaxin-2 complex mediates branching of ductal structures by influencing cell adhesion and gene activation.
History of the Procedure
Surgery for congenital lung malformation was made possible relatively recently. Early 20th century thoracic surgery consisted of mainly thoracoplasty to collapse a tuberculoid lung or to drain an empyema. Only with the regular use of endotracheal intubation and mechanical ventilation in the 1950s did intrathoracic procedures become routine. These techniques were not widely applied to newborns until the 1950s. Although Evarts Graham performed pneumonectomy with mass ligature of the hilum, Churchill was the first to regularly perform lobectomy with hilar dissection. Gross and Lewis successfully treated a patient with congenital lobar emphysema with lobectomy in 1943.
Bronchogenic cysts are increasingly excised thoracoscopically. Rodgers vigorously promoted endoscopic surgery, which has become prevalent with the plethora of new instrumentation available and with the expansion of minimally invasive laparoscopy and thoracoscopy.  Most thoracic surgical procedures, such as resection of masses (eg, neurogenic tumors, bronchogenic cysts) and pulmonary lobectomy, are now accomplished with minimally invasive surgery, although the benefits of this approach for cystic adenomatoid malformations are unclear.
Fetal surgery has been advocated for cystic adenomatoid malformation with hydrops, although it has been abandoned for congenital diaphragmatic hernia (CDH). The extrauterine intrapartum (EXIT) procedure involves delivery of the baby in which the umbilical circulation is left intact if the baby has a congenital high airway obstruction. This procedure allows relief of the obstruction while providing gas exchange across the placenta.
In 2008, RespiRare, a database of children born with congenital lung malformations, was established in France to record patient information and for the prospective collection of clinical data. One recent study looked at the database and found the median gestational age at diagnosis to be 22 weeks.  The malformations were unilateral in all 89 fetuses. Of these neonates, 60% were males. Tachypnea and/or dyspnea were seen in 25% of cases. Only 13% required oxygen therapy, and 11% required ventilation. Polyhydramnios and/or fetal ascites were more specific for severe respiratory distress at birth. Congenital pulmonary malformation volume ratio (CVR) greater than 0.84 was the most sensitive risk factor for oxygen requirement at birth. The authors suggest delivery at a tertiary care center for CVR greater than 0.84, polyhydramnios, and fetal ascites.
Although congenital lung malformations are rare, they are important disorders because they may lead to considerable morbidity and mortality (eg, infection, hemorrhage, respiratory failure). Prognosis depends on the size of the lesion, and the degree of functional impairment. Small lesions may remain asymptomatic. Failure to recognize a malformation may lead to inappropriate intervention. For example, placement of a chest tube to manage suspected tension pneumothorax in a patient with congenital lobar emphysema may lead to lung contusion and ventilation through the chest tube instead of into the remaining healthy lung.
Healthy lung is composed of an orderly system of tubes (airways) and sacs (airspaces or alveoli) in a strict relationship to pulmonary blood vessels (arterial from the right ventricle and venous return to the left atrium). Also present is a systemic blood supply (aorta to superior vena cava) and lymphatic drainage. Congenital lung malformations arise whenever one or more of these structures are abnormal or when their relationships are altered.
Bronchogenic cysts are also known as foregut duplication. They arise from an abnormal budding of the ventral foregut. Approximately 85% are mediastinal, and 15% are intrapulmonary. The peripheral cysts are multiple and appear late in gestation. They may be filled with air or fluid, or they may have air-fluid levels. The cysts can be central or peripheral. Many are asymptomatic, but incidental findings may be observed on chest radiography. Infection, hemorrhage, and, in rare cases, malignancy can occur. Respiratory distress may result in a stridor or wheeze. Airtrapping may lead to emphysema, atelectasis, or both. Dysphagia, chest pain, and epigastric discomfort can occur. See the images below.
Pulmonary agenesis and hypoplasia
Both pulmonary agenesis and hypoplasia may be accompanied by renal anomalies, which are usually apparent soon after birth and associated with respiratory distress. Cardiac defects occur in 50% of patients.
Pulmonary agenesis is differentiated from lung aplasia by the absence of the carina in the latter. Lung agenesis is less common than aplasia, about 75% of cases affect the left side, and it is lethal in half of all patients. It may be associated with other manifestations of the syndrome of abnormalities of the vertebrae, anus, cardiovascular tree, trachea, esophagus, renal system, and limb buds (VACTERL syndrome). The survival rate is better with left-sided lung agenesis than with right-sided agenesis because the right lung is the larger of the two.
In pulmonary hypoplasia, development of the distal lung tissue is incomplete. The earlier the delivery of a child, the higher the incidence of lung hypoplasia. In babies delivered before 28 weeks' gestation, the incidence approaches 20%. Pulmonary hypoplasia results from conditions that restrict lung growth, such as oligohydramnios, Potter syndrome (with bilateral renal agenesis or dysplasia), abnormalities of the thoracic cage, Scimitar syndrome (right-sided pulmonary hypoplasia), and diaphragmatic hernia (usually left-sided hypoplasia). More than 50% of patients have associated cardiac, gut, or skeletal malformations. They may have a small thoracic cage, decreased breath sounds on the affected side, and a mediastinal shift to the side of the lesion. Therefore, aplasia of the right lung can be confused with dextrocardia. Patients may present with lung infections, dyspnea upon exertion, and/or scoliosis.
Pulmonary isomerism is an anomaly of the number of lung lobes. In the common variety of pulmonary isomerism, the right lung has 2 lobes, whereas the left has 3. This anomaly may be associated with situs inversus, asplenia, polysplenia, and/or anomalous pulmonary drainage.
An azygous lobe is a malformation of the right upper lobe caused by an aberrant azygous vein suspended by a pleural mesentery. An azygous lobe is a radiographic curiosity without clinical significance that occurs in 0.5% of the general population.
Pulmonary sequestration accounts for 6% of all congenital lung malformations and mostly occurs in the lower lobes. A sequestration is a bronchopulmonary mass without a normal bronchial communication and with normal or anomalous vascular supply. Sequestered lung may be intralobar or extralobar. The involved lung segments can be classified on the basis of their pleural coverage into intrapulmonary or extrapulmonary types. Variants of pulmonary sequestration are described as disconnected or abnormally communicative bronchopulmonary masses with normal or anomalous vascular supply. The lesions may have some sort of communication with the gut.
Children present with recurrent respiratory problems in the same anatomic location. Associated anomalies include diaphragmatic hernia and eventration. Patients may have exercise intolerance if they have large systemic arterial venous shunts. The extrathoracic variety can be associated with hydrops fetalis or increased lymphatic transudate in the thorax.
About 50% of pulmonary sequestration cases are intrapulmonic, and 60% of intrapulmonic cases occur in the left lower lobe with equal sex distributions. Patients with intrapulmonary sequestration usually present late. They may have a chronic cough, recurrent pneumonias, or poor exercise performance. Systemic arterial flow may produce a murmur, and shunts may lead to congestive cardiac failure. Squamous cell carcinoma, adenocarcinoma, and rhabdomyosarcoma may arise in the sequestration.
Approximately 95% of extrapulmonary cases are left sided. Most extrapulmonary cases are detected in infancy, with boys affected 4 times more than girls. Infants usually present with a chronic cough and recurrent chest infections. Radiographs may reveal signs of consolidation. If communication with the gut is present, children may present with vomiting, failure to thrive due to poor oral intake, and abdominal pain.
The constant feature of this syndrome is partial or total anomalous pulmonary venous return to the inferior vena cava. This abnormal vein on the chest radiography creates a gentle curve bulging into the right chest from the mediastinum that some believe resembles the Turkish sword called a scimitar. Other features of the syndrome are variable and may include dextrocardia, hypoplasia of the right lung and/or pulmonary artery, malformation of the bronchi, and systemic arterial supply to the right lung. The clinical features vary according to age. Infants almost always present with congestive heart failure and severe pulmonary hypertension. Adults are generally asymptomatic.
Hamartomas are lung nodules contain cartilage, respiratory epithelium, and collagen. They may be in the lung tissue or the bronchial lumen. They are presumed to be congenital because they are usually found on chest radiographs in asymptomatic adults. They can cause airway obstruction and are usually excised for diagnosis.
Pulmonary arteriovenous malformation
Pulmonary arteriovenous malformations are abnormal communications between the pulmonary arterial and venous systems without interposed capillaries. Arteriovenous malformations with a systemic arterial supply are unusual in the lung. As with arteriovenous malformations elsewhere, they can lead to high-output cardiac failure. Symptoms are unusual in childhood. However, by adulthood, 50% of patients have at least exertional dyspnea. Hemoptysis is most common in patients who also have cutaneous telangiectasis. A continuous bruit is often heard over the lesion.
The fistulas are usually seen as well-defined opacities on chest radiography, and are multiple in as many as 50% of patients and bilateral in 10%. Most of the fistulas are subpleural, and more often occur in the lower lobes. CT findings are usually diagnostic. Complications include bleeding, infection, and embolus. Patients with cutaneous telangiectasis are likely to have Rendu-Osler-Weber disease (also known as hereditary hemorrhagic telangiectasia). They are likely to have multiple pulmonary arteriovenous malformations and progressive symptoms. Treatment is resection. If this is not possible, the lesions can be embolized.
Alveolar capillary dysplasia
In alveolar capillary dysplasia, a fatal condition, the distal arteriolar blood supply is reduced, the pulmonary veins are misaligned, and the connective tissue between the alveolar epithelium and the capillary endothelium is increased. The alveolar circulation is impaired, and the response to nitric oxide is poor. Affected babies do well with venoarterial extracorporeal membrane oxygenation (ECMO), but they cannot be weaned from it.
The clinical presentation of alveolar capillary dysplasia is that of persistent pulmonary hypertension of the newborn. Hypoxemia leads to arteriolar muscular hypertrophy. Patients may have associated anomalies in the heart or urinary system. Open lung biopsy and cardiac catheterization are suggested as diagnostic tools to look for or exclude pulmonary capillary blush.
Pulmonary lymphangiectasis is a rare disorder in which the normal pulmonary lymphatics are dilated. It may be associated with congenital heart disease in which the pulmonary venous pressure is elevated. Pulmonary lymphangiectasis can also be observed with lymphangiomatosis, in which proliferation of the lymphatic tissue and channels occurs. The disease can also be part of a syndrome of lymphangiomas in many organs; it is sometimes associated with vanishing bones. Pulmonary lymphangiectasis is congenital, but symptoms of respiratory insufficiency usually do not appear until adulthood.
Congenital lobar emphysema
Massive overinflation of one or more lung lobes occurs postnatally in congenital lobar emphysema. Causes include intrinsic absence or abnormality (bronchomalacia) of cartilaginous rings or external compression by a large pulmonary artery. (Compression of the cartilage usually leads to malacia.) Hyperexpansion of a pulmonary lobe is present after birth when, with negative inspiratory pressure, air can enter the lung. However, the air cannot exit easily because positive pressure causes the softened airway to collapse. The remaining normal lung is then compressed.
Congenital lobar emphysema primarily involves the upper lobes. The left upper lobe is involved in 41% of patients; the right middle lobe, in 34%; and the right upper lobe, in 21%. Involvement of the lower lobes is rare, occurring in fewer than 5% of patients. Congenital cardiac anomalies may be present in as many as 10% of patients. Lesions most commonly occur in whites, in male individuals (male-to-female ratio, 3:1), and in young infants.
Most patients with congenital lobar emphysema present before 6 months of life. Neonates may present with mild-to-moderate respiratory distress. Mediastinal shift may be present, with hyperresonance and decreased breath sounds on the involved side. Infants present with cough, wheezing, respiratory distress, and cyanosis. Older children may present with recurrent chest infections. On images obtained in neonates, the affected lobe may be slightly opacified, rather than lucent, because it is still filled with fluid. Associated cardiac anomalies occur in as many as 10% of patients. See the images below.
Cystic adenomatoid malformation
Cystic adenomatoid malformation is a defect in the development of the terminal bronchioles. A hamartomatous proliferation of cysts occurs and resembles bronchioles (airways without cartilage).
Cystic adenomatoid malformation accounts for 25% of all congenital lung malformations. Respiratory distress occurs in the neonatal period, when collateral pores of Kohn ventilate the alveolar tissue present. This process is responsible for the cystic appearance on radiographs. Patients may have mediastinal shift and a pneumothorax. The affected area is dull on percussion, and air entry is decreased. The radiographic depiction of a solid or cystic mass on one side of the thorax suggests the diagnosis.
Three histologic categories of cystic adenomatoid malformation are described: (1) macrocystic (13%), which has the best prognosis and in which one or more large (>5 mm on prenatal ultrasound) cysts are lined with normal pseudostratified ciliated epithelium; (2) microcystic (73%), which has small cysts lined with ciliated columnar or cuboidal epithelium; and (3) solid cystic adenomatoid malformation (13%), which has the worst prognosis and is an airless tissue mass composed of cuboidal epithelium-lined bronchioles. The difference in prognosis may be because the solid and microcystic lesions involve a relatively large amount of lung tissue. Macrocystic lesions are comprised of large, air filled, nonfunctioning spaces involving smaller areas of lungs.
Polyhydramnios may be present if the cystic adenomatoid malformation presses on the esophagus. Pressure on the heart and large vessels may lead to hydrops fetalis. In approximately 60% of patients, cystic adenomatoid malformation manifests soon after the neonatal period. It results in recurrent infections because the mucociliary clearance is poor. Malignancy can occur in the cystic adenomatoid malformation (pulmonary blastoma, rhabdomyosarcoma, and bronchoalveolar carcinoma). See the images below.
Lung cysts are rare lesions that may arise from any of the parenchymal tissues of the lung. They can cause symptoms if they enlarge and occupy substantial space. Resection is performed to diagnose lung cyst and to stop the progression of symptoms.
In a polyalveolar lobe, the number of alveoli increased to more than 3 times normal. The alveoli are counted microscopically in random lung sections. When extra lung fluid is retained, respiratory distress may occur in the first days of life. This generally benign anomaly may be associated with some cases of congenital lobar emphysema.
Congenital lung malformations represent 5-18.7% of all congenital anomalies. This range may be an underestimate because of the high frequency of undetected or asymptomatic lesions.
Bronchogenic cysts represent outpouchings of the ventral foregut in the early part of gestation. These outpouchings generally arise close to the bronchial tree. A cyst may become infected, or it may compress adjacent structures to produce signs and symptoms. Chronic infection and inflammation may predispose the patient to malignancy. Peripheral cysts appear late in gestation and are multiple.
In lung agenesis, the entire lung and bronchial tree may be absent on one side. The bronchial tree may form without development of the alveoli. Pulmonary hypertension complicates lung agenesis because of a combination of factors: normal blood volume passing through reduced lung tissue, hypoxemia leading to pulmonary vasoconstriction, and any associated left-to-right shunting cardiac lesion.
Intrathoracic or extrathoracic lesions can cause pulmonary hypoplasia. Therefore, prolonged rupture of membranes, renal dysplasia, neuromuscular diseases, and congenital diaphragmatic hernia can lead to lung hypoplasia. Reduced urine volume during fetal life may retard lung growth.
Secondary pulmonary causes include cystic adenomatoid malformation and sequestrations. Secondary extrapulmonary, intrathoracic causes include congenital diaphragmatic hernia, hydrothorax, pleural effusions, and tetralogy of Fallot (due to poor lung blood flow). Extrathoracic causes include renal dysplasia and neuromuscular disorders (ie, poor breathing). Bilateral renal agenesis leads to oligohydramnios and poor development of the terminal airways secondary to decreased swallowing of the amniotic fluid. The urinary proline aids in the formation of collagen by the fetal lung. Thyroid transcription factors also regulate lung development. The lung hypoplasia in congenital diaphragmatic hernia is complicated by pulmonary hypertension.
Pulmonary aplasia leads to respiratory distress, which may vary according to the degree of alveolar involvement. Pulmonary hypoplasia may be primary when the entire lung or when one lobe is reduced in size.
If an accessory lung bud forms early enough, it leads to the formation of sequestration in the normal lung tissue. Development late in gestation leads to extrapulmonic sequestration. Both types obtain their blood supply from the aorta or its branches. Patients may present with exercise intolerance due to these vascular shunts. Sequestrations may also be connected to the GI tract.
Congenital lobar emphysema
Causes of congenital lobar emphysema include bronchial cartilage deficiency, extrinsic compression by a bronchogenic cyst, a large pulmonary artery, or mucus plugs. Lobar overdistention and airtrapping lead to compressive changes in the rest of the lung.
Cystic adenomatoid malformation
Cystic adenomatoid malformation results when the terminal bronchiolar component of the advancing endodermal lung bud proliferates haphazardly because of disruption of humoral factors from the surrounding mesenchyme. Apoptosis in the advancing lung bud is decreased. Glial cell–derived neurotrophic factor is a growth factor that is abnormally expressed in the epithelial cells of the cystic adenomatoid malformation. Cystic adenomatoid malformations usually appear before 7 weeks' gestation but can occur in the mid stage of lung development. The growth is thought to plateau at 28 weeks' gestation.  Communication with the normal airways can lead to overinflation and compression of the surrounding lung tissue. The larger the sonographic volume of cystic adenomatoid malformation in relation to head circumference, the greater the chance for developing hydrops because of more severe central venous compression.
Resection is recommended because of the potential for infection, hemorrhage, and respiratory compromise. Resection is especially important in the peripheral lesions, which are usually multiple. These can frequently be excised thoracoscopically because they seldom have a major blood supply.
Pulmonary agenesis and pulmonary hypoplasia
Patients with pulmonary agenesis and pulmonary hypoplasia seem to have one of 3 presentations. The first group consists of patients with insufficient lung tissue who may have received mechanical ventilation for some time. However, ventilator-induced lung injury results in slow decompensation and death. The second group of patients is identified serendipitously when chest radiography is obtained to assess a minor complaint. These patients require no intervention. The third group does not have respiratory distress requiring mechanical ventilation, but they have respiratory limitations to activity or kinking of the airway with shift of the lung to the contralateral side of the chest. In addition to the aplasia or hypoplasia, congenital narrowing of the upper airway also affects many patients.
Resection is recommended, even in asymptomatic patients, to prevent infection, hemorrhage, shunting from arteriovenous anastomoses, or compression of normal lung mass leading to respiratory distress. Lobectomy can usually be performed. For patients with intralobar sequestration, segmentectomy may suffice. Segmentectomy is relatively difficult, but preserves additional functioning lung tissue.
Since the advent of staplers, most surgeons wedge out the lesion with staplers rather than perform the tedious dissection and stripping of segmentectomy that is prone to air leakage and often bloody. In many sequestrations, the mass is airless and separate from the other lung tissue. The surgeon must remain vigilant in searching for the systemic arterial supply. Its origin cannot be predicted, and it may be from below the diaphragm. Bleeding from inadvertently crossing this vessel may be troublesome or even dangerous. For this reason, some surgeons insist on obtaining an arteriogram before surgery.
At least a few thoracoscopic surgeons have accomplished pulmonary resection, even in children. In children, the difficulty in finding enough space in the chest to work while the lungs are being ventilated and the risk of injuring the delicate pulmonary vessels has limited wide adoption of this technique.
When symptoms of scimitar syndrome are related to anomalous pulmonary venous return, this return can be redirected surgically. Symptoms are often related to the bronchial abnormalities and chronic infection. In these cases, pneumonectomy is indicated.
Hamartoma and pulmonary arteriovenous malformation
Resection is usually performed for diagnosis when a lesion is noted on chest radiography. Symptoms of airway obstruction or high cardiac output are occasionally indications for surgery as well.
Congenital lobar emphysema
Progressive airtrapping leads to respiratory and circulatory compromise in infancy. Emergency lobectomy may be required. A patient with respiratory distress whose chest radiograph reveals a hyperlucency on one side and mediastinal shift usually has a tension pneumothorax. However, one must consider congenital lobar emphysema (CLE), especially in the newborn. The diagnosis can usually be determined by looking at the edges of the hyperlucent area. In pneumothorax, the edges are convex and outline the chest wall, whereas in congenital lobar emphysema, they are concave and outline the cystic structure of an overexpanded lobe.
Placing a chest tube in the hyperlucent airspace of congenital lobar emphysema decreases ventilation as air takes the path of least resistance out the chest tube from the bronchus rather than expanding the stiff infant lung in the remaining lobes. Prompt thoracotomy relieves the pressure inside a hyperexpanded lobe and allows the other compressed areas to ventilate. This overexpansion often stretches and dissects the bronchi and vessels, facilitating lobectomy. In cases that are detected early or surgically treated because of radiographic findings and not because of symptoms, the abnormal lobe may be difficult to identify during surgery. Therefore, in these cases, radiographs and CT scans must be carefully reviewed preoperatively.
Cystic adenomatoid malformation
In cystic adenomatoid malformation (CAM), resection of even asymptomatic masses is recommended because of the risk for infection, hemorrhage, acute respiratory compromise (which may occur anytime), and neoplastic transformation. This disease is usually segmental; however, as noted for sequestration, lobectomy may reduce morbidity.
During surgery, lung cysts are often found to be cystic adenomatoid malformations (CAMs), though simple cysts do occur. Some lesions can be shelled out or unroofed. If they are not congenital but related to barotrauma, they may communicate directly with small bronchi. In this case, unroofing leads to major air leaks. These lesions can sometimes be controlled with figure-8 sutures, but wedge resection, segmentectomy, or even lobectomy may be required to avoid a bronchopleural fistula.
Fetal intervention for congenital lung malformations
Many centers perform antenatal aspiration of lung cysts. This procedure is often successful in that no lung cyst appears on postnatal chest radiography. However, many cysts observed on antenatal ultrasonography also spontaneously resolve. The few groups who are pursuing open fetal surgery also perform in utero lobectomy to manage cystic adenomatoid malformation if it is associated with fetal hydrops. This is an unusual situation, and the benefits have not yet been determined.
The lungs continue to mature after birth. Embryologic development progresses from the conductive initial lung bud down to the highly functional respiratory alveoli. Major bronchiolar development ceases around 16 weeks' gestation. Vascular beds form, and the basic acinus framework is then laid down from 17-28 weeks' gestation. Alveolar development starts at 24 weeks' gestation and may continue until adolescence. Most of this increase in the alveoli occurs in the first 8 years of life. Aortic branches initially supply the bronchial buds; later, the pulmonary arteries take over as the lung develops.
The timing and severity of various insults may determine the resultant lesions. These lesions may vary from complete agenesis to bronchial stenosis and sequestration of a lung lobe with retention of the aortic flow. Peripheral pulmonary lesions, such as congenital lobar emphysema (CLE), appear late in development.
Other theories try to account for the abnormal lung vessel communications. The vascular traction theory suggests that the lung tissue is sequestered when the systemic blood vessels move caudally. Another theory is that the pulmonary vessels fail to develop and lead to abnormal persistence of systemic vessels.
Bronchogenic cysts are most commonly mediastinal in a pericarinal, paratracheal, or retrocardiac location. The cysts are thin walled and lined with columnar epithelium. The common central cysts represent outpouchings of the ventral foregut in the early part of gestation.
Pulmonary agenesis and hypoplasia
The entire lung and bronchial tree may be absent on one side. The bronchial tree may form without development of the alveoli. Agenesis is a primary defect in organogenesis, and hypoplasia is often secondary to extrinsic compression. Both lesions may be associated with other anomalies. In physiologic terms, the 2 lesions behave similarly.
Schechter has pointed out the many possible variations. In addition to absence of the entire lung and bronchial tree, an interrupted bronchial tree may be present, but the alveoli are absent or the lung may be reduced in size, or one lobe may be absent.
Pulmonary hypertension complicates lung agenesis because of a combination of factors, including normal blood volume passing through reduced lung tissue, hypoxemia leading to pulmonary vasoconstriction, and any associated left-to-right shunting cardiac lesion.
In pulmonary isomerism, the lungs are asymmetric, and the number of lobes on both sides may vary. Associated findings may include situs inversus and splenic anomalies. Anomalous pulmonary venous drainage is almost always present.
A constant feature of Scimitar syndrome is aplasia of one or more lobes of the right lung. Variable features include the following:
Partial anomalous pulmonary venous return (scimitar-shaped vein) draining to the inferior vena cava and leading to a left-to-right shunt
Small pulmonary artery
Arterial supply from aorta
Anomalies of hemidiaphragm on affected side
Rib cage anomalies
Pulmonary sequestration may be present in the normal lung or outside it, in the thoracic cavity, in the diaphragm, or in a subdiaphragmatic position. Alveoli and bronchioles have normal histology. However, they do not communicate with the normal airways, or they may have an abnormal communication with the gut. Sequestration is fundamentally an abnormal vascular supply to the affected lung, and accelerated atherosclerosis may be found in vessels exposed to high systemic pressures. Branches from the descending thoracic aorta supply the intralobar sequestration, which is drained by pulmonary veins. An infradiaphragmatic source may supply the extralobar variety in as many as 20% of patients, and the azygous venous system drains it.
Congenital lobar emphysema
In congenital lobar emphysema, a single lobe is commonly involved. The bronchi at the involved site may be devoid of cartilage. The number of alveoli may be fewer than normal (hypoalveolar) or greater than normal (polyalveolar). Cardiac anomalies may be present in 10% of patients. The lung parenchyma is normal, unlike what is seen in cystic adenomatoid malformation (CAM).
Cystic adenomatoid malformation
One lobe, multiple lobes, or multiple segments on both sides may be affected. The upper lobes are usually involved. The bronchiolar proliferation is terminal without much alveolar development. The abnormal hamartomatous proliferation usually retains its communication with the normal bronchiolar tree. However, no cartilage or bronchiolar tubular glands are present in the malformation itself. Columnar mucinous epithelium is present.
Three types of congenital lobar emphysema have been identified. In type I, one or more cysts of 2-10 cm are accompanied by smaller cysts, which cysts can become infected. The cysts are lined with pseudostratified columnar epithelium. Mucin is produced. The most common presentation includes respiratory distress caused by overdistention and mediastinal shift. In type II, multiple 0.5-cm to 2-cm cysts are lined with cuboidal epithelium. The cysts resemble bronchioles. Type II is commonly associated with other congenital anomalies, like renal agenesis and dysplasia, prune belly syndrome, undescended testes, pectus excavatum, and syringomyelia. In type III, a solid mass (< 5 cm) consists of microscopic cysts. Types II and III can be associated with sequestration and receive blood supply from systemic arteries.
In a study of 12 patients with late-onset cystic adenomatoid malformation, 7 had type I cystic adenomatoid malformation, and 4 had type II cystic adenomatoid malformation. 
General contraindications include severe sepsis and bleeding disorders. Specific contraindications are discussed below.
Lung cysts usually do not need to be differentiated for surgical purposes because the presentations and outcomes are the same. However, resection is not feasible in cases of diffuse bilateral pulmonary lymphangiectasis manifesting as cystic disease of the lung because the outcome is often poor.
Severe pulmonary hypertension may be a contraindication to operate in cases of pulmonary hypoplasia resulting from congenital diaphragmatic hernia. Associated anomalies may modify the course and the surgical procedures.
Resistant congestive cardiac failure may need to be stabilized before surgical resection is undertaken. This stabilization may necessitate the use of a heart-lung machine.
Congenital lobar emphysema
Congenital lobar emphysema (CLE) poses no specific contraindications and the prognosis after surgery is generally excellent. Surgery may not be required in asymptomatic patients, for whom close follow-up usually suffices.
Cystic adenomatoid malformation
Fetal hydrops is the only consistent predictor of mortality associated with cystic adenomatoid malformation (CAM). Cystic adenomatoid malformation may be a contraindication for postnatal surgery.
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