Published online November 10, 2003, 10.1148/rg.e17
(Radiographics. 2003;24:e17.)
© RSNA, 2003
Congenital Anomalies of the Tracheobronchial Tree, Lung, and Mediastinum: Embryology, Radiology, and Pathology1
Teresa Berrocal, MD, PhD,
Carmen Madrid, MD,
Susana Novo, MD,
Julia Gutiérrez, MD,
Antonia Arjonilla, MD and
Nieves Gómez-León, MD, PhD
1 From the Department of Pediatric Radiology, Hospital Infantil La Paz, 261 Paseo de la Castellana, 28046 Madrid, Spain. Presented as an educational exhibit at the 2002 RSNA scientific assembly. Received April 21, 2003, revision requested July 2, revision received and accepted August 13. Address correspondence to T.B. (e-mail: cprieto@hulp.insalud.es).
 |
Abstract
|
|---|
Congenital anomalies of the chest are an important cause of morbidity in infants, children, and even adults. The evaluation of affected patients frequently requires multiple imaging modalities to diagnose the anomaly and plan surgical correction. The authors analyze and illustrate practical aspects of certain common and uncommon congenital anomalies affecting the tracheobronchial tree, lung, and mediastinum, with emphasis on radiologic manifestations. Other thoracic anomalies such as rib anomalies and vascular rings are discussed when they are associated with anomalies of the tracheobronchial tree. The usefulness of the various imaging modalities in the diagnosis and treatment of these conditions is also evaluated. Specific topics addressed include tracheal conditions such as tracheal stenosis, tracheomalacia, tracheal bronchus, tracheal atresia, and bronchogenic cyst; anomalies of the lung such as lung underdevelopment (agenesis and hypoplasia), scimitar syndrome, congenital cystic adenomatoid malformation, congenital lobar emphysema, and pulmonary sequestration; esophageal anomalies such as esophageal atresia, tracheoesophageal fistula, and esophageal duplications; and vascular rings. The embryologic and pathologic basis of the radiologic findings are discussed in appropriate cases. Differential diagnoses, as well as pitfalls and diagnostic difficulties, are included.
© RSNA, 2003
Index Terms: Bronchi, abnormalities, 671.1412, 671.1441, 671.1499 • Esophagus, abnormalities, 71.141, 71.142 • Lung, abnormalities, 60.141, 60.142, 60.145, 60.146, 60.1499 • Trachea, abnormalities, 671.1493, 671.1499 • Trachea, stenosis or obstruction, 671.1414, 671.1499
|
Embryology
|
|---|
The respiratory system develops from the ventral wall of the foregut during gestation at 3–4 weeks (embryonic stage) and continues development during the first 2 years of life and beyond. The epithelium of the trachea, bronchi, and alveoli originates from the endoderm; muscle, cartilage, and connective tissue originate from the mesoderm (1,2). The tracheobronchial tree develops between days 24 and 36 of gestation. A median bulge develops on the ventral wall of the pharynx at the laryngotracheal groove at days 24–26 (3). While the laryngotracheal groove is forming, there is a proliferation of the mesenchyme of the primitive mesentery (mediastinum); from this mesenchyme, the cartilage, muscle, and connective tissue of the lungs will develop (2). By the 28th day, the bulge has formed into the right and left lung buds. As the lung buds elongate, lateral invagination of the mesoderm constitutes the tracheoesophageal septum, which separates the esophagus and trachea (2–4). The separation of alimentary and respiratory structures is not always completed successfully. Defective or incomplete separation is one of the most frequent congenital anomalies (2). At 28–30 days, the lung buds continue to elongate, forming the primary bronchi, which develop monopodial outgrowths that lengthen into the segmental bronchi. At the same time, the tissue vascular supply shifts from the splenic plexus to the definite pulmonary arteries (3,4).
The life of a human lung can be subdivided into five distinct phases: embryonic, pseudoglandular, canalicular, saccular, and alveolar. The embryonic period, during which the lung primordium is laid down as a diverticulum of the foregut, lasts about 7 weeks. From the 5th to the 17th week, the lung looks much like a tubuloacinar gland, with epithelial tubes sprouting and branching into the surrounding mesenchyme. In the last week of this pseudoglandular stage, the prospective conductive airways have been formed and the acinar limits can be recognized. The events of the subsequent canalicular phase (weeks 17–26) can be summarized as the widening of the peripheral tubules, differentiation of the cuboidal epithelium into type I and type II cells, formation of the first thin air-blood barriers, and start of surfactant production. During the saccular stage, which follows and lasts until birth, the growth of the pulmonary parenchyma, thinning of the connective tissue between the airspaces, and further maturation of the surfactant system are the most important steps toward independent life. At birth, although already functional, the lung is structurally still in an immature condition, because alveoli, the gas exchange units of the adult lung, are practically missing. The airspaces present are smooth-walled transitory ducts and saccules with primitive type septa that are thick and contain a double capillary network. During the first 1–3 years of postnatal life, alveoli are formed through a septation process that greatly increases the gas exchange surface area. The primitive septa with their capillaries undergo a complete remodeling, gaining the mature slender morphology found in the adult lung (5).
The right lung grows faster than the left, being both larger and having more generations of bronchial branching. At approximately 10 weeks, cartilage appears in the trachea and primary bronchi and at 16 weeks in the segmental bronchi (2,5). At this time, all nonrespiratory airway branches are present and the bronchial branches are widely separated by mesenchyme (1). Up to 16 weeks, during the "glandular stage," the pulmonary mesenchyme is solid and the distal portions of the developing bronchial tree show little or no evidence of lumen. At 24 weeks, during the "alveolar stage," the distal ends of the ducts open and the alveoli are formed (6). The peripheral respiratory epithelium begins to differentiate into type 1 and type 2 pneumocytes at approximately 23–24 weeks gestation (type 2 pneumocytes produce surfactant) (1,6). After 24 weeks, there is an apparent decrease in the number of generations of bronchi due to epithelial changes in terminal bronchioles and their conversion into respiratory bronchioles (5). After 28 weeks of gestation, there is a marked decrease in mesenchymal tissue, the distal airway saccules subdivide, and their walls become thinner. Alveoli first appear at approximately 32 weeks gestation and are usually present by 36 weeks. Alveoli continue to multiply until 300 million have formed. This number is reached when the child is about 8 years old. Alveolar size continues to increase until the adult thoracic cavity configuration is attained. Between 16 and 28 weeks, development and vascularization of the acinus occur. The pulmonary artery develops from the sixth aortic arch and gives off branches that parallel the development of the airways (preacinar vessels) and the alveoli (intraacinar vessels). By the end of the 16th week, the preacinar vessels are formed and supply the capillary bed of the respiratory tissue. Most of the growth and development of intraacinar vessels occurs after birth and follows the rate of alveolar development (5,7).
In the embryonic stage, a diffuse vascular plexus develops in the mesenchyme and divides into pulmonary and esophageal components. This plexus forms a capillary network that fuses with the pulmonary arterial branches during the late embryonic stage and gives rise to the pulmonary venous system. Ultimately, an outpouching of the sinoatrial region of the heart (common pulmonary vein) connects with this venous plexus. The common pulmonary vein becomes incorporated into the many pulmonary veins that drain into the left atrium (1).
Classification of the congenital anomalies of the tracheobronchopulmonary apparatus is difficult and controversial, not only from an embryologic and morphologic standpoint but from a pathologic and clinic viewpoint (2).
|
Tracheobronchial Anomalies
|
|---|
Tracheomalacia
Tracheomalacia is defined as tracheal wall softening due to an abnormality of the cartilaginous ring and hypotonia of the myoelastic elements. Tracheomalacia exists when the cartilaginous framework of the trachea is unable to maintain airway patency. The cartilage in the airway of infants is normally soft, and therefore all infants have some degree of dynamic collapse during expiration, when the pressure outside the trachea exceeds the pressure inside. In tracheomalacia, dynamic collapse leads to airway obstruction (14,15). Primary tracheomalacia is thought to be caused by congenital immaturity of the tracheal cartilage. In secondary tracheomalacia, previously normal cartilage undergoes degeneration (14). The congenital variety may be associated with other developmental defects such as a vascular ring or tracheoesophageal fistula (Fig 1) (16,17). All types of tracheomalacia are rare; to our knowledge, no definite prevalence rates are available. The condition may on occasion be symptomatic. The symptoms and treatment are similar to those of asthma.
View larger version (112K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 1a. Tracheomalacia. (a) Radiograph of the trachea in a 2-month-old infant with stridor shows marked diffuse tracheal narrowing during expiration (arrows). (b, c) Radiographs of a 3-week-old infant with Hurler disease. The trachea (arrows) was noted to be persistently narrowed in all studies.
|
|
View larger version (83K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 1b. Tracheomalacia. (a) Radiograph of the trachea in a 2-month-old infant with stridor shows marked diffuse tracheal narrowing during expiration (arrows). (b, c) Radiographs of a 3-week-old infant with Hurler disease. The trachea (arrows) was noted to be persistently narrowed in all studies.
|
|
View larger version (111K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 1c. Tracheomalacia. (a) Radiograph of the trachea in a 2-month-old infant with stridor shows marked diffuse tracheal narrowing during expiration (arrows). (b, c) Radiographs of a 3-week-old infant with Hurler disease. The trachea (arrows) was noted to be persistently narrowed in all studies.
|
|
Tracheomalacia commonly involves most of the trachea and other major airways. Symptoms of tracheomalacia include wheeze, cough, stridor, dyspnea, tachypnea, cyanosis, and recurrent respiratory tract infections. Congenital diffuse malacia of the airway improves by age 6–12 months, as the structural integrity of the trachea is restored gradually. Lateral fluoroscopy and esophagography may be diagnostic. Fluoroscopy shows an exaggerated decrease in the caliber of the trachea during expiration. Wheezing is loudest during crying or forced expiration. Cine computed tomography (CT) has provided dynamic cross-sectional evaluation of tracheal compliance and regional anatomy.
Tracheal Stenosis
Congenital tracheal stenosis is a rare disorder characterized by the presence of focal or diffuse complete tracheal cartilage rings, resulting in a fixed tracheal narrowing. The entity may be seen in isolation or in conjunction with other anomalies, the most common of which is the pulmonary artery sling complex (8–10). Pulmonary artery sling is a rare congenital anomaly in which the left pulmonary artery originates from the right pulmonary artery and encircles the right mainstem bronchus and distal trachea, causing compression of each (8–10). One must be aware of this anomaly when examining an infant with apparent segmental distal tracheal stenosis. A variety of congenital stenosis patterns have been described, along with a variety of different surgical approaches. Approximately 50% of congenital tracheal stenoses are focal, 30% generalized, and 20% funnel-shaped (11). Focal congenital tracheal stenosis consists of a simple local narrowing of the trachea, usually in the lower third. The distal end of the trachea and bronchi are of normal size. Symptoms are variable, depending on the age of the child, the degree of stenosis, and the potential presence of associated anomalies. Infants in whom this disorder is discovered early in life tend to have a worse prognosis (12). Ninety percent of children present during the 1st year of life, often with biphasic stridor. Length of stenosis does not appear to be as critical as degree of stenosis in producing symptoms, as airway resistance is only linearly proportional to length of stenosis, whereas resistance increases fourfold relative to luminal radius decrease. Determining the cause of fixed intrinsic tracheal narrowing in a symptomatic child is crucial. Frontal and lateral high-kilovoltage filtered radiographs are easily obtained and advantageously show the entire airway (9,11) (Fig 2). Because of ionizing radiation, CT should be used only in selected cases.
View larger version (80K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 2a. Tracheal stenosis. (a) Posteroanterior and (b) lateral radiographs of the upper airways show narrowing of the tracheal lumen in the subglottic trachea (arrows). (c) Curvilinear coronal reformation of CT scan shows the narrowed segment (arrows) (1 = craniocaudal length of the stenosis, 2 = transverse diameter of the tracheal lumen at the stenosis). (d) Posteroanterior radiograph of the trachea in another patient, obtained with filtered high-kilovoltage technique, shows two tracheal narrowings (arrows).
|
|
View larger version (108K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 2b. Tracheal stenosis. (a) Posteroanterior and (b) lateral radiographs of the upper airways show narrowing of the tracheal lumen in the subglottic trachea (arrows). (c) Curvilinear coronal reformation of CT scan shows the narrowed segment (arrows) (1 = craniocaudal length of the stenosis, 2 = transverse diameter of the tracheal lumen at the stenosis). (d) Posteroanterior radiograph of the trachea in another patient, obtained with filtered high-kilovoltage technique, shows two tracheal narrowings (arrows).
|
|
View larger version (97K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 2c. Tracheal stenosis. (a) Posteroanterior and (b) lateral radiographs of the upper airways show narrowing of the tracheal lumen in the subglottic trachea (arrows). (c) Curvilinear coronal reformation of CT scan shows the narrowed segment (arrows) (1 = craniocaudal length of the stenosis, 2 = transverse diameter of the tracheal lumen at the stenosis). (d) Posteroanterior radiograph of the trachea in another patient, obtained with filtered high-kilovoltage technique, shows two tracheal narrowings (arrows).
|
|
View larger version (126K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 2d. Tracheal stenosis. (a) Posteroanterior and (b) lateral radiographs of the upper airways show narrowing of the tracheal lumen in the subglottic trachea (arrows). (c) Curvilinear coronal reformation of CT scan shows the narrowed segment (arrows) (1 = craniocaudal length of the stenosis, 2 = transverse diameter of the tracheal lumen at the stenosis). (d) Posteroanterior radiograph of the trachea in another patient, obtained with filtered high-kilovoltage technique, shows two tracheal narrowings (arrows).
|
|
These studies combined with barium esophagography usually allow a correct diagnosis. If necessary, helical CT or electron-beam CT can be useful for evaluating dynamic changes in the airway (9). Magnetic resonance (MR) imaging is valuable for demonstrating the relationship of the airway to adjacent blood vessels without injection of intravascular contrast medium. Both CT and MR imaging can provide three-dimensional reconstruction (13).
Tracheal Bronchus
Tracheal bronchus was described by Sandifort in 1785 as a right upper bronchus originating in the trachea (3). The term tracheal bronchus includes a variety of bronchial anomalies arising in the trachea or main bronchus and directed toward the upper-lobe territory. This anomalous bronchus usually exits the right lateral wall of the trachea less than 2 cm above the major carina and can supply the entire upper lobe or its apical segment (3,18–20). Tracheal bronchus may be displaced or supernumerary (Fig 3a). If the anatomic upper-lobe bronchus is missing a single branch, the tracheal bronchus is defined as displaced; if the right upper-lobe bronchus has a normal trifurcation into apical, posterior, and anterior segmental bronchi, the tracheal bronchus is defined as supernumerary (1–3,19). The supernumerary bronchi may end blindly; in that case, they are also called tracheal diverticula. If they end in aerated or bronchiectatic lung tissue, they are termed apical accessory lungs or tracheal lobes (2,19,20). Right tracheal bronchus has a prevalence of 0.1%–2% and left tracheal bronchus a prevalence of 0.3%–1% in bronchographic and bronchoscopic studies (3,21). Patients are usually asymptomatic, but the diagnosis of tracheal bronchus should be considered in cases of persistent or recurrent upper-lobe pneumonia, atelectasis or air trapping, and chronic bronchitis. Bronchiectasis, focal emphysema, and cystic lung malformations may coexist (3,18,21). The prevalence of tracheal bronchus in association with infantile lobar emphysema is unknown, but the association is more frequent with left tracheal bronchus (22). Diagnosis of this entity should be considered early in the clinical course of intubated patients with right-upper-lobe complications (18,20,22). Tumoral lesions developing in a tracheal bronchus are infrequent; a few cases have been reported in the English language literature (20). Most of these bronchial branching anomalies are well diagnosed at chest CT as a small area of hypoattenuation arising directly from the trachea (3,20,23) (Fig 3b, 3c).
View larger version (85K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 3a. Tracheal bronchus. (a) Drawing shows the most frequent origin of the tracheal bronchus (arrows). (b) CT section demonstrates a right-upper-lobe bronchus (arrows) arising from the trachea, above the carina. (c) CT scan of the same patient at the level of the carina, 2 cm below the origin of the tracheal bronchus. (d) Bronchogram helps confirm the diagnosis and shows the origin of the tracheal bronchus. Rib alterations in the right hemithorax are secondary to prior thoracotomy.
|
|
View larger version (64K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 3b. Tracheal bronchus. (a) Drawing shows the most frequent origin of the tracheal bronchus (arrows). (b) CT section demonstrates a right-upper-lobe bronchus (arrows) arising from the trachea, above the carina. (c) CT scan of the same patient at the level of the carina, 2 cm below the origin of the tracheal bronchus. (d) Bronchogram helps confirm the diagnosis and shows the origin of the tracheal bronchus. Rib alterations in the right hemithorax are secondary to prior thoracotomy.
|
|
View larger version (66K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 3c. Tracheal bronchus. (a) Drawing shows the most frequent origin of the tracheal bronchus (arrows). (b) CT section demonstrates a right-upper-lobe bronchus (arrows) arising from the trachea, above the carina. (c) CT scan of the same patient at the level of the carina, 2 cm below the origin of the tracheal bronchus. (d) Bronchogram helps confirm the diagnosis and shows the origin of the tracheal bronchus. Rib alterations in the right hemithorax are secondary to prior thoracotomy.
|
|
View larger version (152K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 3d. Tracheal bronchus. (a) Drawing shows the most frequent origin of the tracheal bronchus (arrows). (b) CT section demonstrates a right-upper-lobe bronchus (arrows) arising from the trachea, above the carina. (c) CT scan of the same patient at the level of the carina, 2 cm below the origin of the tracheal bronchus. (d) Bronchogram helps confirm the diagnosis and shows the origin of the tracheal bronchus. Rib alterations in the right hemithorax are secondary to prior thoracotomy.
|
|
The displaced type of tracheal bronchus is more frequent than the supernumerary type. This fact may be well demonstrated with high-resolution spiral CT, which can demonstrate that the aberrant bronchus may correspond to a segmental, subsegmental, or subsubsegmental bronchus (3). Bronchography and bronchoscopy allow the direct visualization of the ectopic bronchus (Fig 3d).
Most patients with tracheal bronchus can be treated conservatively; however, in symptomatic patients surgical excision of the involved segment is necessary (24).
Bronchial Atresia
Congenital bronchial atresia is a rare anomaly that results from focal obliteration of a proximal segmental or subsegmental bronchus that lacks communication with the central airways. The development of distal structures is normal (1,25,26). Bronchial atresia most often affects segmental bronchi at or near their origin; however, lobar or subsegmental bronchi may also be involved. The bronchi distal to the stenosis become filled with mucus and form a bronchocele. The alveoli supplied by these bronchi are ventilated by collateral pathways and show features of air-trapping, resulting in a region of hyperinflation around the dilated bronchi (25,27). In some cases, bronchial atresia may be acquired postnatally owing to traumatic or postinflammatory insult to the bronchus (1). The upper-lobe bronchi are more frequently affected; middle and lower lobes are rarely affected (25). The abnormality is an incidental finding in approximately 50% of cases, mostly in young men, and generally produces no symptoms or signs.
In the newborn period, bronchial atresia is seen as a water-density mass. The mass is fetal lung liquid trapped behind the atresia. Later in childhood, the fetal lung liquid escapes and bronchial atresia is found because of focal air trapping. The short atretic segment leads to accumulation of mucus within the distal bronchi to form a bronchocele, and underventilation of the affected part of the lung occurs. In adults, bronchial atresia characteristically is seen as a solitary pulmonary nodule due to a mucus plug and less frequently as congenital lobar emphysema (25). Bronchial atresia is usually asymptomatic and is found incidentally in chest radiographs; however, dyspnea, pneumonia, and bronchial asthma have been reported (25). The characteristic chest radiographic finding consists of a bronchocele, seen as rounded, branching opacities radiating from the hilum. The bronchocele may contain an air-fluid level. The distal lung is emphysematous and produces an area of hyperlucency around the affected bronchi. In newborns, the affected segment may be seen as a fluid-filled mass (25). CT is a sensitive modality for demonstrating the typical features of bronchial atresia. It shows a round opacity at the site of the atresia, medial to the air trapping, which can be clearly depicted by performing expiratory CT (28) (Fig 4).
View larger version (109K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 4a. Bronchial atresia (a) CT scan shows air trapping in the right upper lobe (arrows). (b) CT scan in the same patient shows a round opacity at the site of the atresia, medial to the air trapping, representing mucoid impaction just distal to the atresia.
|
|
View larger version (107K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 4b. Bronchial atresia (a) CT scan shows air trapping in the right upper lobe (arrows). (b) CT scan in the same patient shows a round opacity at the site of the atresia, medial to the air trapping, representing mucoid impaction just distal to the atresia.
|
|
CT is an excellent modality for excluding the presence of a hilar mass and precisely determining delineation and location of lesions. In doubtful cases, multiplanar reformation helps distinguish mucoid impaction from nodular lesions. When the location is basal, spiral CT with contrast medium injection can easily exclude a vascular component, which could indicate pulmonary sequestration (28). MR imaging usually shows the bronchocele as a branching structure radiating from the hilum, with high signal intensity in T1- and T2-weighted images; however, MR imaging cannot depict regional air trapping.
Bronchogenic Cyst
Bronchopulmonary foregut malformations are anomalies of pulmonary development that are due to abnormal budding of the embryonic foregut and tracheobronchial tree. This abnormality includes foregut cysts, bronchogenic cysts, enteric cysts, and neuroenteric cysts (29–31).
Bronchogenic cysts are congenital lesions thought to originate from the primitive ventral foregut and may be mediastinal, intrapulmonary, or, less frequently, in the lower neck. Approximately two-thirds are within the mediastinum, and one-third are intraparenchymal (29,32,33). They account for 40%–50% of all congenital mediastinal (intrathoracic) cysts, and there is a slight male predominance. The frequency of bronchogenic cysts is unknown presumably because most patients are asymptomatic. Numerous studies have documented the rare frequency of bronchogenic cysts, with an average incidence of 20 cases over a 20-year period. The cysts contain mucoid material and are lined by ciliated columnar or cuboidal epithelium. Their walls contain smooth muscle and often cartilage. They are sometimes intrapulmonary, typically in the medial third of the lung. If in a mediastinal location, they may be paratracheal (usually right-sided), carinal, or hilar. The carinal location is most frequent. They also can be found in the posterior and anterior mediastinum (in the latter location, it may be necessary to distinguish them from other more frequent anterior mediastinal cysts such as cystic teratoma, thymic cysts, or cysts derived from ectopic thyroids glands) (31,33).
Bronchogenic cysts do not initially communicate with the tracheobronchial tree. Instrumentation of the cyst or infection may lead to air-filled cyst or an air-fluid level. Two-thirds of the patients are symptomatic; symptoms are due to the size and position of the cyst. Symptoms are most frequently caused by compression of the trachea or bronchi, which leads to cough, wheezing, stridor, dyspnea, cyanotic spells, and pneumonia. Infection occurs in 20% of patients with intraparenchymal cysts, usually secondary to communication with the tracheobronchial tree (34). However, most bronchogenic cysts in children are found incidentally when imaging is performed for other reasons
Bronchogenic cysts are rarely detected with prenatal sonography. To our knowledge, the first case reported in the medical literature was by Avni et al in 1986 (35). They usually seen as a unilocular, fluid-filled cyst in the middle or posterior mediastinum. Differential considerations include esophageal duplication cyst, neuroenteric cyst and congenital cystic adenomatoid malformation (36). Intrapulmonary bronchogenic cysts are usually located in the lower lobes (37). In infants and children, the chest radiograph is diagnostic for bronchogenic cysts in three out of four cases (32). The cysts are filled with serous or mucous fluid, so usually appear as water-density mass lesions in chest radiographs (Fig 5).
View larger version (156K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 5a. Bronchogenic cyst. (a) Chest radiograph of an asymptomatic 5-year-old girl shows a large soft-tissue mass in the right hemithorax (arrows). (b) Contrast material-enhanced CT scan through the upper lobes shows a well-defined water-density homogeneous mass (*) with no contrast enhancement.
|
|
View larger version (106K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 5b. Bronchogenic cyst. (a) Chest radiograph of an asymptomatic 5-year-old girl shows a large soft-tissue mass in the right hemithorax (arrows). (b) Contrast material-enhanced CT scan through the upper lobes shows a well-defined water-density homogeneous mass (*) with no contrast enhancement.
|
|
Intrapulmonary cysts may communicate with the tracheobronchial tree and then may show air or an air-fluid level (Fig 6).
View larger version (134K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 6a. Complicated bronchogenic cyst. (a) Chest radiograph shows rounded mass with an air-fluid level, occupying the entire right middle lobe, corresponding to a bronchogenic cyst connecting with the bronchus. (b) Contrast-enhanced CT scan shows a thick-walled fluid-filled rounded mass (*) with an air-fluid level, corresponding to the infected bronchogenic cyst. Note enhancement of the cystic wall.
|
|
View larger version (120K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 6b. Complicated bronchogenic cyst. (a) Chest radiograph shows rounded mass with an air-fluid level, occupying the entire right middle lobe, corresponding to a bronchogenic cyst connecting with the bronchus. (b) Contrast-enhanced CT scan shows a thick-walled fluid-filled rounded mass (*) with an air-fluid level, corresponding to the infected bronchogenic cyst. Note enhancement of the cystic wall.
|
|
CT has the capability of locating an intrathoracic cyst, defining its extent and relation to key structures, and characterizing the intrinsic density (35) (Fig 5b). The cyst has variable attenuation values. The density of mucus-containing cyst is often higher than that of water; this also may be due to the presence of calcium in the cyst fluid (33,35). The cysts show no contrast enhancement, but when they become infected they may show wall enhancement (Fig 6b).
T1-weighted MR images show that the intrinsic signal intensity ranges from low to high depending on cyst contents. On T2-weighted MR images, the cysts are typically high in signal intensity (29,36). The possibility of malignancy should be considered when a solid component is seen in a cyst wall at CT or MR imaging (33).
|
Anomalies of the Lung
|
|---|
Pulmonary Underdevelopment
Pulmonary underdevelopment has been classified into three groups by Schneider and Schwalbe (40). In group 1, bronchus and lung are absent (agenesis); in group 2, a rudimentary bronchus is present and limited to a blind-end pouch without lung tissue (aplasia); and in group 3, there is bronchial hypoplasia with variable reduction of lung tissue (hypoplasia) (1,28).
Pulmonary agenesis occurs during the embryogenic period (approximately 4 weeks gestation), when the primitive lung is forming. The etiology of lung agenesis is unknown, although genetic, teratogenic, and mechanical factors have been proposed as possible causes. The abnormality is usually unilateral, and there is no side or gender predominance (40,41). More than 50% of children with pulmonary agenesis have associated congenital anomalies that involve the cardiovascular (more frequent patent ductus arteriosus and patent foramen ovale), gastrointestinal, skeletal, and genitourinary systems. Most of the limb and spinal anomalies are ipsilateral to the pulmonary agenesis, whereas the rib anomalies are variable. The contralateral lung is normal in structure but has compensatory hypertrophy. Patients with right-lung agenesis have a shorter life expentancy than those with left-lung agenesis; this suggests that the right-lung agenesis has a greater frequency of an associated shift of the heart and mediastinum, with corresponding distortion of bloods vessel and bronchi (37,38). The diagnosis of lung agenesis is usually first suspected at chest radiography that demonstrates a small, completely opaque hemithorax with displacement of the mediastinal structures and diaphragm (Fig 7).
View larger version (88K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 7a. Lung agenesis. (a) Schematic of lung agenesis. (b) Posteroanterior and (c) lateral radiographs of a 5-year-old boy with complete opacity of the right hemithorax and displacement of the heart and mediastinum to the right. Note the tracheal displacement to the right. (d) Bronchography and (e) pulmonary angiography in the same patient demonstrate complete absence of the main right pulmonary bronchus and artery, with normal left arteries and bronchial branches
|
|
View larger version (165K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 7b. Lung agenesis. (a) Schematic of lung agenesis. (b) Posteroanterior and (c) lateral radiographs of a 5-year-old boy with complete opacity of the right hemithorax and displacement of the heart and mediastinum to the right. Note the tracheal displacement to the right. (d) Bronchography and (e) pulmonary angiography in the same patient demonstrate complete absence of the main right pulmonary bronchus and artery, with normal left arteries and bronchial branches
|
|
View larger version (136K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 7c. Lung agenesis. (a) Schematic of lung agenesis. (b) Posteroanterior and (c) lateral radiographs of a 5-year-old boy with complete opacity of the right hemithorax and displacement of the heart and mediastinum to the right. Note the tracheal displacement to the right. (d) Bronchography and (e) pulmonary angiography in the same patient demonstrate complete absence of the main right pulmonary bronchus and artery, with normal left arteries and bronchial branches
|
|
View larger version (175K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 7d. Lung agenesis. (a) Schematic of lung agenesis. (b) Posteroanterior and (c) lateral radiographs of a 5-year-old boy with complete opacity of the right hemithorax and displacement of the heart and mediastinum to the right. Note the tracheal displacement to the right. (d) Bronchography and (e) pulmonary angiography in the same patient demonstrate complete absence of the main right pulmonary bronchus and artery, with normal left arteries and bronchial branches
|
|
View larger version (112K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 7e. Lung agenesis. (a) Schematic of lung agenesis. (b) Posteroanterior and (c) lateral radiographs of a 5-year-old boy with complete opacity of the right hemithorax and displacement of the heart and mediastinum to the right. Note the tracheal displacement to the right. (d) Bronchography and (e) pulmonary angiography in the same patient demonstrate complete absence of the main right pulmonary bronchus and artery, with normal left arteries and bronchial branches
|
|
Ocasionally, the agenesis may be confined to one lobe, most frequently the left upper lobe (Fig 8).
View larger version (166K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 8a. Lung agenesis of the left upper lobe. (a) Posteroanterior and (b) lateral chest radiographs of a girl with opacity of the left upper lobe (white arrows) and displacement of the mediastinum to the left. Note the compensatory hyperinflation of the left lower lobe. There are various hemivertebra (black arrows) and small left ribs.
|
|
View larger version (136K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 8b. Lung agenesis of the left upper lobe. (a) Posteroanterior and (b) lateral chest radiographs of a girl with opacity of the left upper lobe (white arrows) and displacement of the mediastinum to the left. Note the compensatory hyperinflation of the left lower lobe. There are various hemivertebra (black arrows) and small left ribs.
|
|
A normal contralateral lung with compensatory hyperinflation and herniation across the midline is a usual finding. Abnormal segmentation of the thoracic vertebral bodies also may be present (Fig 8). Bronchography verifies that the mainstem bronchus is completely missing, and angiography demonstrates the absence of pulmonary and bronchial arteries on the side of the absent lung (Fig 7d). Conventional CT, MR imaging, and angiography may provide important diagnostic information, showing the absence of lung parenchyma, bronchial tree, and pulmonary vessels on the affected side (Fig 7e) (1,38). CT angiography and MR angiography are currently the imaging modalities of choice in the diagnosis of this entity, with angiography used only in selective cases.
Pulmonary hypoplasia is defined as deficient or incomplete development of the lungs (39). It is characterized by the presence of both bronchi and alveoli in an underdeveloped lobe, and it is caused by factors directly or indirectly compromising the thoracic space available for lung growth (40), such as a congenital diaphragmatic hernia in which a defect of the hemidiaphragma allows the abdominal viscera to herniate into the thoracic cavity with compression of the ipsilateral lung. Pulmonary hypoplasia also is noted in extralobar sequestration, agenesis of the diaphragm, large pleural effusion, and Jeune syndrome (asphyxiating thoracic dystrophy), a rare entity in which a small and rigid thoracic cage produces a decrease in lung volume. The extrathoracic causes include oligohydramnios (Potter syndrome: renal agenesis, abnormal fasciae, limb anomalies, and bilateral pulmonary hypoplasia), in which the mechanism of development is unknown but is thought to be predominantly compression of the fetal thorax by the uterus. Other causes include decreased pulmonary vascular perfusion (tetralogy of Fallot, unilateral absence of the pulmonary artery). Intrathoracic causes, such as a congenital diaphragmatic hernia, are the most common (1,39). The true prevalence is unknown, but in cases of premature rupture of membranes at 15–28 weeks gestation, the reported prevalence of pulmonary hypoplasia ranges from 9% to 28%.
The most common manifestation is early respiratory distress after birth, cyanosis, tachypnea, hypoxia, hypercapnea, and acidosis. Pneumothorax and pulmonary hypertension are common serious complications. Pneumothorax often develops spontaneously or secondary to mechanical ventilation. The degree of pulmonary hypoplasia depends on the volume and duration of the cause. Plain radiographs demonstrate decreased aeration of the affected hemithorax (more frequent in the right lung) and a small thoracic cage (Fig 9).
View larger version (99K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 9a. Pulmonary hypoplasia. (a) Schematic illustrates pulmonary hypoplasia. (b) Anteroposterior chest radiograph of a 7-month-old infant shows opacity of the left hemithorax and small left lung (arrows) with ipsilateral displacement of the mediastinum, secondary to repaired Bochdaleck hernia.
|
|
View larger version (127K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 9b. Pulmonary hypoplasia. (a) Schematic illustrates pulmonary hypoplasia. (b) Anteroposterior chest radiograph of a 7-month-old infant shows opacity of the left hemithorax and small left lung (arrows) with ipsilateral displacement of the mediastinum, secondary to repaired Bochdaleck hernia.
|
|
A common finding is a displacement of the mediastinum to the side of the hypoplasia, accentuated during inspiration because there is increased compensatory ventilation of the other lung (41) (Figs 9, 10). In some cases, a cystic appearance is encountered, which could be due to a developmental defect at the bronchioloalveolar junction, leading to an appearance of congenital bronchiectasis. Differential diagnosis must then be made with congenital cystic adenomatoid malformation (28). The prenatal diagnosis of pulmonary hypoplasia with ultrasound is difficult. The recent application of MR imaging may provide additional valuable information. With this modality, we are able to assess the volume of normal ipsilateral and contralateral lung. Normal pulmonary tissue has homogeneously high signal intensity. In fetuses with lung hypoplasia, a decrease in signal intensity has been reported (41,42).
View larger version (154K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 10a. Pulmonary hypoplasia. (a) Anteroposterior radiograph shows opacity of the right hemithorax and a shift of the mediastinal structures to the right, due to pulmonary hypoplasia secondary to right diaphragmatic agenesis. (b) Angiographic MR image of a 10-year-old boy shows a hypoplastic right pulmonary artery (arrows).
|
|
View larger version (156K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 10b. Pulmonary hypoplasia. (a) Anteroposterior radiograph shows opacity of the right hemithorax and a shift of the mediastinal structures to the right, due to pulmonary hypoplasia secondary to right diaphragmatic agenesis. (b) Angiographic MR image of a 10-year-old boy shows a hypoplastic right pulmonary artery (arrows).
|
|
Scimitar Syndrome
The scimitar syndrome, also called venolobar syndrome and hypogenetic lung syndrome, is a rare congenital cardiovascular anomaly involving the right lung. In its complete form, the syndrome consists of ipsilateral anomalous pulmonary drainage of part or all of the right lung into the inferior vena cava, hypoplasia of the right lung (Fig 11), dextrorotation of the heart, hypoplasia or other malformation of the right pulmonary artery, and anomalous systemic arterial supply to the lower lobe of the right lung from the subdiaphragmatic aorta or its main branches (43,44).
View larger version (81K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 11a. Scimitar syndrome. (a) Schematic illustrates the characteristic findings of the scimitar syndrome. (b) Chest radiograph shows decreased aeration of the right hemithorax and displacement of the heart and mediastinum to the right. There is loss of the right heart shadow due to the right pulmonary hypoplasia and to the pulmonary vein coursing to the right cardiophrenic angle (scimitar sign) (arrows). (c) Angiographic MR image shows the anomalous vein draining into the inferior vena cava (arrows). (d) Angiographic MR image of a patient after surgery for scimitar syndrome. Note the anomalous vein draining now into the right atrium (arrow).
|
|
View larger version (156K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 11b. Scimitar syndrome. (a) Schematic illustrates the characteristic findings of the scimitar syndrome. (b) Chest radiograph shows decreased aeration of the right hemithorax and displacement of the heart and mediastinum to the right. There is loss of the right heart shadow due to the right pulmonary hypoplasia and to the pulmonary vein coursing to the right cardiophrenic angle (scimitar sign) (arrows). (c) Angiographic MR image shows the anomalous vein draining into the inferior vena cava (arrows). (d) Angiographic MR image of a patient after surgery for scimitar syndrome. Note the anomalous vein draining now into the right atrium (arrow).
|
|
View larger version (116K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 11c. Scimitar syndrome. (a) Schematic illustrates the characteristic findings of the scimitar syndrome. (b) Chest radiograph shows decreased aeration of the right hemithorax and displacement of the heart and mediastinum to the right. There is loss of the right heart shadow due to the right pulmonary hypoplasia and to the pulmonary vein coursing to the right cardiophrenic angle (scimitar sign) (arrows). (c) Angiographic MR image shows the anomalous vein draining into the inferior vena cava (arrows). (d) Angiographic MR image of a patient after surgery for scimitar syndrome. Note the anomalous vein draining now into the right atrium (arrow).
|
|
View larger version (147K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 11d. Scimitar syndrome. (a) Schematic illustrates the characteristic findings of the scimitar syndrome. (b) Chest radiograph shows decreased aeration of the right hemithorax and displacement of the heart and mediastinum to the right. There is loss of the right heart shadow due to the right pulmonary hypoplasia and to the pulmonary vein coursing to the right cardiophrenic angle (scimitar sign) (arrows). (c) Angiographic MR image shows the anomalous vein draining into the inferior vena cava (arrows). (d) Angiographic MR image of a patient after surgery for scimitar syndrome. Note the anomalous vein draining now into the right atrium (arrow).
|
|
The scimitar syndrome is also associated with abnormal systemic blood supply to the right lung, abnormal bronchial anatomy, abnormal diaphragm, hemivertebrae, and anomalies of the genitourinary tract. Scimitar syndrome is usually right-sided; however, rare cases have been reported that involved the left side (44,45). Three forms of scimitar syndrome have been described. In the infantile form, there is a large shunt between the abnormal artery that supplies the lower lobe of the right lung and the subdiaphragmatic aorta; this is sometimes called sequestration. In the adult form, there is a small shunt between the right pulmonary veins and inferior vena cava. The third form is characterized by additional cardiac and extracardiac malformations (43).
The clinical significance and prognosis of scimitar sydrome depend to a large extent on the amount of the resulting left-right shunt; at least 40% of patients are asymptomatic. This syndrome may be discovered when patients undergo routine chest radiography. The clinical symptoms usually manifest in the 2nd to 3rd decade of life, with fatigue and dyspnea with exertion being most common and recurrent pulmonary infection less common (1). In the infantile group, a higher prevalence of pulmonary hypertension has been reported (44). The diagnosis is based on chest radiography, ultrasonography, CT, and MR imaging (43–46). The radiographic appearance of the pulmonary vein descending along the right cardiac border is characteristic (scimitar sign) (1,45) (Fig 11b). The vein may not be visible if it is small or obscured by the heart shadow. The aberrant vein is located posteriorly in lateral chest radiographs. CT may show the size of the right hemithorax, bronchial anomalies, and the anomalous vein. Doppler ultrasonography may show the entrance of the anomalous vein into the inferior vena cava and can verify the venous flow. Angiography may identify the aberrant vein, showing the size of the right pulmonary artery (1). Several reports have described the feasibility of noninvasive techniques, such as cine MR imaging and contrast-enhanced angiographic MR imaging for evaluation of this syndrome (Fig 11c, 11d). This technique offers excellent visualization of pulmonary vascular anatomy (46).
Congenital Cystic Adenomatoid Malformation
Congenital cystic adenomatoid malformation of the lung is an uncommon cause of respiratory distress in neonates and infants. It is characterized by a multicystic mass of pulmonary tissue with an abnormal proliferation of bronchial structures (41). Pathogenetically, congenital cystic adenomatoid malformation has been attributed to an overgrowth of bronchioles, with almost complete suppression of alveolar development between the 7th and 10th weeks of embryonic life (2,47) This malformation was classified by Stoker et al (48) into three histologic types. Type I is composed of variable-size cysts, with at least one dominant cyst (>2 cm in diameter) (Figs 12, 13). This is the most common (75%) form.
View larger version (159K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 12a. Type I congenital cystic adenomatoid malformation. (a) Anteroposterior and (b) lateral chest radiographs of a newborn show a multicystic mass occupying the right hemithorax (note the variable size of the cysts, some of them >2 cm) (arrows).
|
|
View larger version (159K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 12b. Type I congenital cystic adenomatoid malformation. (a) Anteroposterior and (b) lateral chest radiographs of a newborn show a multicystic mass occupying the right hemithorax (note the variable size of the cysts, some of them >2 cm) (arrows).
|
|
View larger version (153K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 13a. Type I congenital cystic adenomatoid malformation. (a) Anteroposterior chest radiograph of a 5-year-old child shows a bubbly mass in the left upper lobe with a dominant air cyst morre than 4 cm in diameter (arrows). (b) CT scan of the same patient shows a hypoattenuating, clearly delineated cystic mass (*) in the left upper lobe.
|
|
View larger version (119K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 13b. Type I congenital cystic adenomatoid malformation. (a) Anteroposterior chest radiograph of a 5-year-old child shows a bubbly mass in the left upper lobe with a dominant air cyst morre than 4 cm in diameter (arrows). (b) CT scan of the same patient shows a hypoattenuating, clearly delineated cystic mass (*) in the left upper lobe.
|
|
A type II congenital cystic adenomatoid malformation is composed of smaller, more uniform cysts less than 1 cm in diameter (10% to 15% of all congenital cystic adenomatoid malformations) (Fig 14).
View larger version (166K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 14a. Type II congenital cystic adenomatoid malformation. (a) Anteroposterior chest radiograph of a newborn shows a heterogeneous bubbly mass in the left lung displacing mediastinal structures to the right. (b) Coronal T1-weighted image in the same patient shows cysts (arrows) smaller than 2 cm in diameter. (c) In another newborn patient, chest CT shows a complex cystic mass in the right upper lobe, smaller than the type I mass seen in Figure 13b.
|
|
View larger version (184K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 14b. Type II congenital cystic adenomatoid malformation. (a) Anteroposterior chest radiograph of a newborn shows a heterogeneous bubbly mass in the left lung displacing mediastinal structures to the right. (b) Coronal T1-weighted image in the same patient shows cysts (arrows) smaller than 2 cm in diameter. (c) In another newborn patient, chest CT shows a complex cystic mass in the right upper lobe, smaller than the type I mass seen in Figure 13b.
|
|
View larger version (104K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 14c. Type II congenital cystic adenomatoid malformation. (a) Anteroposterior chest radiograph of a newborn shows a heterogeneous bubbly mass in the left lung displacing mediastinal structures to the right. (b) Coronal T1-weighted image in the same patient shows cysts (arrows) smaller than 2 cm in diameter. (c) In another newborn patient, chest CT shows a complex cystic mass in the right upper lobe, smaller than the type I mass seen in Figure 13b.
|
|
A type III congenital cystic adenomatoid malformation is a solid mass composed of bronchoalveolar microcysts (Fig 15).
View larger version (165K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 15. Type III congenital cystic adenomatoid malformation. Anteroposterior chest radiograph of a premature girl weighing 700 g shows an irregular microcystic mass affecting the left lung and displacing the mediastinum to the right. There is an associated dextrocardia.
|
|
Type III congenital cystic adenomatoid malformation often causes death at birth (41,48,49). The natural history and prognosis of congenital cystic adenomatoid malformation are variable, depending on the size rather than histologic type of the lesion (41). There is broad variation in prenatal presentation of congenital cystic adenomatid malformation, ranging from an incidental finding at routine prenatal ultrasonography to severe hydrops with mass effect and mediastinal shift. The differential diagnosis includes congenital diaphragmatic hernia, pulmonary sequestration, and bronchogenic cysts. Among infants in whom the malformation is diagnosed postnatally, one-half to two-thirds will have some form of respiratory distress or compromise, including tachypnea, retractions, and cyanosis (32). The presentation in older patients is usually recurrent pulmonary infections. In older patients, cysts have an inflammatory component not found in children; this is due to the respiratory-lining and mucin-secreting cells. Congenital cystic adenomatoid malformation usually involves a single lobe, multilobar involvement being infrequent (50).
The postnatal diagnosis is made with plain chest radiography, which demonstrates multiple air-filled thin-walled cysts that vary in size. Unlike in diaphragmatic hernia, the distribution of abdominal bowel gas is normal. Air-fluid levels may be seen with or without superimposed infection. In severe cases, the lung may be hyperexpanded, with mediastinal shift, a flat hemidiaphragm, and herniation of the lung to the contralateral side. CT can be useful for characterizing congenital cystic adenomatoid malformation by showing its location and extent (Figs 13b, 14c), and for differentiating it from congenital lobar emphysema and bronchogenic cysts. In older infants and children with recurrent infections, this condition must be differentiated from necrotizing pneumonia. Recurrent infection in the same site, hyperexpansion of the affected lobe, and absence of air bronchograms favor the former diagnosis (49).
Congenital Lobar Emphysema
Congenital lobar emphysema is characterized by progressive overdistention of a lobe, sometimes two lobes. It is thought to result from a check-valve mechanism at the bronchial level that causes progressive hyperinflaction of the lung by allowing more air to enter the involved area on inspiration than leaves on expiration (51–54). The most commonly affected lobe is the left upper lobe, followed by the middle lobe. The distribution of lobar involvement is 42.2% in the left upper lobe, 35.3% in the right middle lobe, 20.7% in the right upper lobe, and 0.9% in each lower lobe (52). There is no destruction of alveolar walls. In 50%–55% of cases, the cause of congenital lobar emphysema is unknown, although areas of malacia or stenosis of the bronchial cartilage were found in these patients and these are considered the most likely explanations (52,53). Congenital lobar emphysema may be associated with other anomalies (cardiovascular system is involved in 12%–14%) (51,52). It is more common among males than females; it is not familial and occurs predominantly in Caucasians
Top
Abstract
Embryology
