Congenital Lung Anomalies

Chapter 53

Congenital Lung Anomalies

Congenital lung anomalies refer to a heterogeneous group of pulmonary developmental disorders that affect the lung parenchyma, the arterial supply, and the venous drainage to the lung, or a combination of these entities. The reported incidence of congenital lung anomalies ranges from 1.2 : 10,000 to 1 : 35,000 pregnancies; however, these reports may be an underestimate of their true incidence.13 Although prenatal sonography (ultrasound), advances in postnatal imaging, and, more recently, fetal magnetic resonance imaging (MRI) have enhanced our understanding of congenital lung anomalies, substantial controversy continues regarding the nomenclature, classification, pathogenesis, description, and management of these lesions. In addition, considerable variability exists in their prenatal clinical presentation and outcome, ranging from in-utero involution to severe hydrops and fetal demise. Likewise, their postnatal clinical presentation also is variable, ranging from the completely asymptomatic newborn to the older child or young adult with recurrent pneumonias. In this chapter, the underlying etiology, clinical presentation, imaging findings, and management of various congenital lung anomalies encountered in the pediatric population are discussed.

Spectrum of Congenital Lung Anomalies

The classification of congenital lung anomalies is challenging and continuously controversial from embryologic, radiologic, pathologic, and clinical viewpoints. Several classifications and terminologies with their own advantages and disadvantages have been suggested.46 Some investigators have used embryology as a basis and have classified congenital lung anomalies according to the stage of intrauterine development in which the insult resulting in the malformation developed.4 Other investigators have categorized lesions based on their morphologic-radiologic features and divided them into two groups: whole lung malformations (e.g., lung hypoplasia) and focal malformations (e.g., bronchial atresia).5,7 Recently the Langston6 classification has become one of the most accepted classification systems for congenital lung anomalies, particularly from the pathological standpoint, although it is by no means the most widely used classification by all clinical groups. Langston categorizes the wide spectrum of respiratory tract malformations primarily as bronchial atresia, congenital pulmonary airway malformation (CPAM), extralobar bronchopulmonary sequestration (BPS), congenital lobar hyperinflation (CLH), and bronchogenic cysts. These five congenital lung anomalies comprise approximately 90% of the anomalies seen in clinical practice. However, this classification system is limited because other congenital lung anomalies (e.g., pulmonary arteriovenous malformation [AVM]) are not included.

For the purpose of relatively clear classification, easy differentiation on imaging studies, and preoperative assessment of surgical lesions, congenital lung anomalies discussed in this chapter are categorized according to their morphologic-radiologic-pathologic features. Such a classification system views congenital lung anomalies as a continuum ranging from predominantly parenchymal abnormalities (i.e., abnormal lung parenchyma, relatively normal vasculature, airway, and foregut derivatives, e.g., CPAM), to predominantly vascular abnormalities (i.e., normal lung parenchyma, normal airway, and no foregut abnormality but abnormal vasculature; e.g., AVM), to combined parenchymal and vascular abnormalities (e.g., pulmonary sequestration and scimitar syndrome) in which influencing factors (foregut and airway components) play an important role and the major abnormalities are intertwined (Fig. 53-1).

Given that specific terminology for these lesions may be controversial and occasionally confusing, we and other authors811 recommend that radiologists thoroughly describe all imaging findings of congenital lung anomalies rather than try to categorize the lesions by pathologic terminology. Specific imaging findings of congenital lung anomalies that need to be evaluated and described include (1) location of lesions, (2) associated anomalous vascular supply and drainage of the lesions, (3) internal components and the degree of aeration, (4) exclusion of communication with the gastrointestinal (GI) tract, (5) integrity of the diaphragm, and (6) an assessment of associated anomalies, such as vertebral anomalies.8,10

Predominantly Parenchymal Lesions

Bronchial Atresia

Etiology: Bronchial atresia refers to atresia of a lobar, segmental, or subsegmental bronchus at or near its origin resulting in a blind-ended atretic proximal bronchus. Bronchial atresia most frequently affects a segmental bronchus. The precise etiology of bronchial atresia remains unknown, but etiologies such as a vascular insult to the involved atretic or stenotic portion have been proposed.6,8 Several authors who used modern dissecting techniques found that bronchial atresia is more common than originally thought.6,12,13 Furthermore, bronchial atresia and BPSs coexist in nearly all cases,6,12,13 whereas it is found in nearly 70% of CPAM lesions.12 A malformation sequence resulting from airway obstruction during development has been proposed as the unifying element for such a wide spectrum of imaging appearances. Differences in degree, level, and timing of the bronchial obstruction are thought to be responsible for the association of bronchial atresia and other congenital lung anomalies.6,8,12 Bronchial atresia usually is diagnosed as an incidental finding on chest radiographs later in life in asymptomatic older children or adults.6,10 However, bronchial atresia increasingly is being diagnosed in utero, given the widespread use of prenatal imaging.6,9,10,12,13

Imaging: Prenatally, the involved portion of the lung appears hyperexpanded and shows increased homogenous echogenicity on ultrasound and high T2 signal on fetal MRI14 (Fig. 53-2). On occasion, it is possible to identify the centrally located, mucus-filled bronchocele/mucocele on prenatal ultrasound or MRI9,15 (e-Fig. 53-3).

Characteristically, the apicoposterior segmental bronchus of the left upper lobe is most commonly affected, followed by the segmental bronchi of the right upper, right middle, and lower lobes.16 In children, radiographic and computed tomography (CT) imaging features of bronchial atresia are characterized by a tubular or glove-shaped opacity representing mucus plugging in the region distal to the atretic bronchus, surrounding segmental hyperlucency due to air trapping, and decreased underlying vascularity15,17 (e-Fig. 53-4). However, in neonates, a portion of the lung distal to the atretic segment may remain atelectatic as a result of the in-utero mucostasis. Therefore some authors recommend avoiding immediate postnatal imaging evaluation because the under-aerated lung related to bronchial atresia may be difficult to differentiate from the normal lung with expected fetal fluid retention in the newborn period.10 Identification of the hallmark atretic bronchus and the “bronchocele/mucocele” by means of two-dimensional (2D) multiplanar or three-dimensional (3D) reconstructions either on prenatal or postnatal imaging may be helpful.10,18

Treatment and Follow-up: Management of bronchial atresia is somewhat varied. In general, surgical resection is primarily recommended in symptomatic pediatric patients because of recurrent infection.17,19 Although opinions vary, some centers advocate elective surgical resection of bronchial atresia even in asymptomatic pediatric patients because of potential future lung infection and increased association with CPAM.13,20

Bronchogenic Cysts

Etiology: Bronchogenic cysts result from abnormal tracheobronchial branching and presumably originate from an aberrant bud of the developing foregut, similar to other foregut duplication cysts. Bronchogenic cysts typically are unilocular, fluid-filled, or mucus-filled cysts lined by respiratory epithelium and are attached to but do not communicate with the tracheobronchial tree.6,17,19 Although most bronchogenic cysts are located within the mediastinum (predominantly near the carina), they may be encountered anywhere from the suprasternal area to the retroperitoneum. Bronchogenic cysts also may be found within the lung parenchyma, usually in the lower lobes.17,19 Such intrapulmonary bronchogenic cysts do not communicate with the airway unless superimposed infection with wall necrosis occurs,6 which may further predispose them to recurrent infections. The clinical symptomatology of affected pediatric patients primarily depends on the mass effect the lesion exerts on its neighboring structures including the airway, GI tract, and cardiovascular structures. Airway compression is usually mild, but it may be life threatening in some instances when large bronchogenic cysts are located near the carina regions.21

Imaging: A bronchogenic cyst typically presents as a round or oval-shaped cystic lesion located near the right paratracheal or subcarinal area within the middle mediastinum. Bronchogenic cysts are anechoic on prenatal ultrasound and show high signal intensity on T2-weighted prenatal MRI imaging14,19 (e-Fig. 53-5). On chest radiographs, a bronchogenic cyst manifests as a well-delineated round or oval-shaped middle mediastinal mass. On CT, approximately 50% of bronchogenic cysts demonstrate fluid attenuation value (~0 Hounsfield unit) (Fig. 53-6). The remaining bronchogenic cysts may have CT attenuation higher than water because of thick mucoid, milk-of-calcium, proteinaceous, or hemorrhagic contents. MRI, which can confirm the cystic nature of the bronchogenic cysts on T2-weighted images, is helpful for differentiating bronchogenic cysts with high attenuation value from a mildly enhancing solid mass on CT. Typically, no internal contrast enhancement is seen within the uncomplicated bronchogenic cysts on CT or MRI. The presence of an air-fluid level, thick wall enhancement, or surrounding inflammatory changes often is associated with superimposed infection.11,16,17

Treatment and Follow-up: Complete surgical resection is the current management of choice for bronchogenic cysts, particularly in symptomatic pediatric patients.22 Temporizing or palliative procedures such as transparietal, transbronchial, or mediastinal aspiration may be considered in symptomatic pediatric patients who are not surgical candidates.

Congenital Lobar Hyperinflation

Imaging: On prenatal imaging, CLH manifests as a homogeneously hyperechogenic lesion on ultrasound or as a T2 hyperintense lesion on MRI without visible cysts.9,24 On prenatal imaging, CLH often is indistinguishable from other congenital lung anomalies, particularly bronchial atresia.9,24 CLH usually is diagnosed by its typical clinical presentation and characteristic radiographic features of progressive lobar hyperexpansion and hyperlucency, producing displacement or compression of adjacent structures. In the immediate postnatal period, CLH initially may appear as an area of increased opacity related to retained fetal lung fluid, which will clear on subsequent studies.6,17,19,23 Similar imaging findings are noted on CT, and the attenuated pulmonary vasculature is a helpful clue to distinguish CLH from a pneumothorax or other entities in cases of inconclusive chest radiographic findings17 (Fig. 53-7).

Treatment and Follow-up: Surgical lobectomy is the current management for symptomatic pediatric patients with CLH.22 Some medical centers advocate expectant management for cases with minimal or no symptoms.21,25

Congenital Pulmonary Airway Malformation

Etiology: CPAMs, formerly known as cystic adenomatoid malformations of the lung, were first described in the literature by Ch’In and Tang in 1949 as rare lung lesions occurring in premature or stillborn infants with significant hydrops.26,27 CPAMs are characterized by a heterogeneous group of congenital cystic and noncystic lung masses that communicate with an abnormal bronchial tree lacking supporting cartilage.8,17,28

In 1977, Stocker et al.28 classified these lesions based on their clinical and pathologic features, with subdivisions based on the size of the cysts (types I, II, and III) and according to the location of suspected development of the malformation along the airway. Type I CPAMs consist of cysts larger than 2 cm, with presumed bronchial/bronchiolar origin. Type II CPAMs consist of cysts smaller than 2 cm, with presumed bronchiolar origin. Type III CPAMs appear solid, with a presumed bronchiolar/alveolar origin. However, Stocker later expanded his CPAM classification into five types that included type 0 CPAMs, with presumed tracheobronchial origin, and type IV CPAMs, with presumed distal acinar origin. The term CPAM was now implemented instead of cystic adenomatoid malformations, because cystic changes were observed in only three of the aforementioned types (types, I, II, and IV), and adenomatoid change was observed only in type III.9,17,29,30 Increasing evidence indicates that type IV CPAM lesions and type I pleuropulmonary blastomas may represent the same entity.6,31 It is important to recognize that although Stocker’s classification is widely used, it is by no means universally accepted. For an example, Langston6 classifies CPAM lesions into two types and terms the Stocker type I CPAM as “large cyst type lesions” and the Stocker type II CPAMs as “small cyst type lesions” based on cyst size and pathologic criteria.6 Langston proposed that the type III CPAM actually represents a form of pulmonary hyperplasia and should be excluded from the CPAM classification.

Imaging: Prenatally, CPAMs are classified on the basis of cyst size as microcysts (<5 mm) and macrocysts (≥5 mm) on fetal ultrasound and MRI.32 Type 1 CPAMs may contain one, several, or multiple macrocysts, some of which are ≥5 mm in diameter9 (Fig. 53-8). Type II CPAMs have variable appearances, ranging from homogeneously hyperechoic or hyperintense lesions to microcystic lesions exhibiting multiple, uniform cysts that measure <5 mm9,14,19 (e-Figs. 53-9 and 53-10).

Postnatal imaging findings of CPAMs usually correlate with underlying histopathologic features.17 Large cyst type or type I CPAMs typically present with one or several larger air-filled cystic structures with intervening solid, unaerated lung parenchyma. The cysts of type I CPAMs are larger than 2 cm and may be accompanied by several microcysts, whereas small cyst type or type II CPAMs usually manifest as partially air-filled multicystic masses, with individual cysts smaller than 2 cm and with variable degrees of solid-appearing, unaerated lung tissue.10,17 Type 3 CPAMs typically appear as solid lesions with mild contrast enhancement because of microscopic cysts that can be identified only at histologic evaluation. Type IV CPAMs usually present as large cysts arising from the peripheral portion of the lung and can be radiographically indistinguishable from a predominantly cystic type 1 pleuropulmonary blastoma (see Chapter 55) (e-Fig. 53-11).

In their pure forms, CPAM blood supply is from the pulmonary artery and venous drainage is into the pulmonary veins. Although unilobar involvement of CPAM is far more common, multilobar and even bilateral lung involvement may occur.3,27,30 Although any lobe of the lung can be involved, predilection exists for the lower lobe.3 CPAMs that are complicated as a result of superimposed infection may have an imaging appearance similar to pneumonia or a lung abscess (Fig. 53-12).

Treatment and Follow-up: The generalized consensus is that symptomatic CPAMs should be resected, typically by lobectomy, regardless of the patient’s age at presentation.17,22,33 However, considerable controversy exists with regard to the management of prenatally diagnosed, asymptomatic, small CPAM lesions, and no consensus exists on the timing of34 or need for resection.3539 Although some persons advocate a nonsurgical strategy with imaging follow-up, most medical centers advocate surgical resection before 1 year of age because of the potential risk of associated complications, such as infection, pneumothorax, and the small risk of malignant transformation, particularly in the case of CPAM type I lesions.3,21,22,33,40

Predominantly Vascular Lesions

Anomalies of the Pulmonary Artery

Pulmonary Agenesis, Aplasia, and Hypoplasia

Etiology: Pulmonary underdevelopment may be classified into three main types: (1) lung agenesis, consisting of the absence of the lung, bronchus, and pulmonary artery; (2) lung aplasia, that is, the presence of a rudimentary bronchus but the lack of lung tissue and pulmonary artery; and (3) lung hypoplasia, which consists of a hypoplastic bronchial tree and pulmonary artery with a variable amount of lung parenchyma.17,41

The etiology of lung agenesis or aplasia remains uncertain. Genetic, teratogenic, and mechanical factors may play a role.17 Pulmonary agenesis associated with ipsilateral radial ray defects or hemifacial microsomia may be the result of an abnormal development of the first and second arch derivatives or abnormal blood flow at this level inciting the developmental event, given the common association.42 On the other end of the spectrum, no identifiable cause has been found for lung hypoplasia.17

Persons with pulmonary agenesis, aplasia, and hypoplasia either are asymptomatic or present with variable degrees of respiratory distress, depending on the extent of lung underdevelopment. Associated congenital malformations may be seen in 50% to 80% of cases involving the heart, gastrointestinal tract, skeleton, and vascular and genitourinary systems.17,4244

Imaging: On chest radiographs, affected pediatric patients may or may not present with a small, radiopaque hemithorax, depending on the degree of the abnormality. Ipsilateral displacement of mediastinal structures and elevation of the hemidiaphragm usually are present. The normal contralateral lung shows compensatory hyperinflation and herniation across the anterior midline, which is best seen on the lateral projections as a band of increased retrosternal lucency17 (Fig. 53-13). Left lung agenesis is more common than right lung agenesis. Multidetector CT with multiplanar 2D and 3D imaging capabilities can be used to distinguish among pulmonary agenesis, pulmonary aplasia, and pulmonary hypoplasia by clearly identifying the bronchial stump and/or the rudimentary bronchial tree17,45 (e-Figs. 53-14 and 53-15, Fig. 53-16, and e-Fig. 53-17).

Dec 20, 2015 | Posted by in PEDIATRIC IMAGING | Comments Off on Congenital Lung Anomalies

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