Pediatric Annals

Special Issue Article 

Congenital Lung Malformations

John Palla, MD; Marianna M. Sockrider, MD, DrPH

Abstract

Congenital lung malformations (CLM) comprise a spectrum of anatomical anomalies of the lungs and respiratory tree. The prenatal growth pattern of CLMs is unpredictable with larger lesions causing life-threatening complications, such as hydrops fetalis, and smaller lesions remaining asymptomatic and potentially regressing. The most common CLMs are congenital pulmonary adenomatoid malformations, bronchopulmonary sequestrations, congenital lobar emphysema, and bronchogenic cysts. All these lesions have clinically similar presentations when symptomatic, but pathophysiologic differences that must be considered when evaluating and treating. This article reviews the most common CLMs, their pathophysiology, clinical presentation, diagnostic considerations, and current literature on the controversies surrounding CLM management. [Pediatr Ann. 2019;48(4):e169–e174.]

Abstract

Congenital lung malformations (CLM) comprise a spectrum of anatomical anomalies of the lungs and respiratory tree. The prenatal growth pattern of CLMs is unpredictable with larger lesions causing life-threatening complications, such as hydrops fetalis, and smaller lesions remaining asymptomatic and potentially regressing. The most common CLMs are congenital pulmonary adenomatoid malformations, bronchopulmonary sequestrations, congenital lobar emphysema, and bronchogenic cysts. All these lesions have clinically similar presentations when symptomatic, but pathophysiologic differences that must be considered when evaluating and treating. This article reviews the most common CLMs, their pathophysiology, clinical presentation, diagnostic considerations, and current literature on the controversies surrounding CLM management. [Pediatr Ann. 2019;48(4):e169–e174.]

Congenital lung malformations (CLM) comprise a spectrum of anatomic anomalies involving the lungs and respiratory tree.1,2 These lesions are structural defects characterized by the focal disruption of normal lung development. Their etiology and pathophysiology remain unknown, although all are thought to originate from a disruption in the branching morphogenesis of the airway tree.3 The lesions occur sporadically, have no inheritance pattern, and are rarely associated with other congenital anomalies.3–5 The most common CLMs are congenital pulmonary adenomatoid malformations (CPAM), bronchopulmonary sequestrations (BPS), congenital lobar emphysema (CLE), bronchogenic cysts, and hybrid lesions of CLMs, such as BPS and CPAM.

Congenital lung abnormalities are typically first detected on routine prenatal ultrasound. An abnormal prenatal ultrasound is the most common presentation of CLMs in the United States and Europe.6 Ultrasound findings may include increased echogenicity in the thorax, indirect signs of a mass effect causing cardiac compression, mediastinal shift, contralateral lung hypoplasia, and/or polyhydramnios from esophageal compression.1 The incidence of CLMs identified on prenatal ultrasounds ranges from 1 in 6,000 to 8,000 to 1 in 24,000 to 35,000 in published studies.2,6–9 Lower historical estimates are likely due to improved ultrasound sensitivity rather than an increase in incidence of CLMs.1,9

The prenatal course of CLMs is variable depending on the size of the lesion. Larger lesions may cause life-threatening complications, such as hydrops fetalis. Other lesions, especially smaller ones, may even regress prior to birth. However, the prenatal growth pattern of CLMs is rather unpredictable.1,7 Greater than 90% of fetuses with CLMs do well during pregnancy.1 Most infants are initially asymptomatic at birth.10 In the neonatal period, infants who are symptomatic typically have respiratory distress. In childhood, the predominant symptoms are recurrent infections and/or respiratory distress.10

It is difficult to establish a definitive prenatal diagnosis with absolute certainty based on ultrasound findings due to the similar appearances of different congenital pulmonary and nonpulmonary lesions (ie, malignancy).1,11 Early postnatal imaging is required to identify the presence of any suspected lesion and should be done in all infants suspected to have a CLM.11 CLM patients should be referred to pulmonologists for further evaluation. Initial testing can include ultrasound with doppler, chest radiography, chest computed tomography (CT) with intravenous contrast, or magnetic resonance imaging (MRI) to delineate vasculature and determine whether there is communication of the lesion with the tracheobronchial tree.1 Although typically there are no other associated congenital disorders, such as cardiac anomalies, screening should be done.1

This article reviews the most common CLMs, their pathophysiology, clinical presentation, diagnostic considerations, and current literature on the controversies surrounding CLM management.

Congenital Pulmonary Adenomatoid Malformations

CPAMs, previously known as congenital cystic adenomatoid malformations, are characterized by adenomatoid proliferation of the terminal bronchioles that results in a multicystic mass of pulmonary tissue rather than alveoli.1,12,13 Cyst size, number, and location vary. They are typically unilobar and unilateral but may be found in segments within a single lobe, may cross lobes, be multifocal, and/or bilateral.2,12,13

CPAMs are the most commonly diagnosed type of CLM.12 They have an estimated incidence of 1 in 10,000 to 35,000 with no association to race, sex, maternal age, or genetic predisposition.12,13 CPAMs are thought to develop due to abnormal branching of bronchioles during lung morphogenesis. These lesions typically communicate with the tracheobronchial tree. CPAM blood supply is usually from the pulmonary artery but may arise from the aorta or systemic arteries (similar to pulmonary sequestrations). Therefore, it is important to look postnatally for the presence of an anomalous blood supply.1,12

Stocker et al.,5 in 1977, proposed the first classification system for CPAMs with three types based on cyst size and histopathology. This classification system was later expanded to five types (0–4) to better correlate the arrested lung development at different stages with the findings of resected cysts (Table 1).1,8,12

Congenital Pulmonary Adenomatoid Malformations Classification

Table 1.

Congenital Pulmonary Adenomatoid Malformations Classification

Critics of the Stocker system point to its failure to recognize hybrid lesions that contain features of both CPAMs and BPSs and that it doesn't apply to prenatal screening.13 Thus, Adzick et al.12 proposed another classification system based on prenatal screening findings with only two types (Table 2).14

CPAM Prenatal Screening Classification

Table 2.

CPAM Prenatal Screening Classification

Almost all CPAMs are detected with prenatal ultrasound but one cannot make a definitive diagnosis as this lesion on imaging appears similar to other pulmonary and nonpulmonary lesions, such as congenital diaphragmatic hernia (CDH), pulmonary sequestrations, and malignancies.1,12 Large CPAMs tend to present at birth with respiratory distress due to a mediastinal shift and compression of surrounding lung tissue.1 In newborns with respiratory distress, CDH can have a similar appearance as a CPAM on imaging. Infants with smaller CPAMs are typically asymptomatic at birth and may go on to develop respiratory symptoms later in life, usually with recurrent pulmonary infections. Most CPAMs are diagnosed within the first 2 years of life.1,12

The sensitivity of chest radiographs detecting CPAMs is only 60% (Figure 1), whereas the sensitivity of chest CT is 100%15 (Figure 2). Therefore, it is recommended that all neonates with a prenatal screen concerning for a CPAM, even if asymptomatic, have a postnatal CT scan. Chest MRI is an alternative with lower radiation exposure, but that risk must be weighed against the risk of sedation required for MRI.12,13

Chest radiograph of a 7-day-old girl with congenital pulmonary adenomatoid malformations of the left upper lobe.

Figure 1.

Chest radiograph of a 7-day-old girl with congenital pulmonary adenomatoid malformations of the left upper lobe.

Computed tomography of the chest of a 7-day-old girl with congenital pulmonary adenomatoid malformations of left upper lobe.

Figure 2.

Computed tomography of the chest of a 7-day-old girl with congenital pulmonary adenomatoid malformations of left upper lobe.

There is a growing body of literature describing the potential for malignant transformation of CPAMs leading to the development of lung neoplasms. Both rhabdomyosarcoma and pleuropulmonary blastoma (PPB) have been reported as arising within CPAMs.1 There is histologic overlap between a CPAM type 4 and a grade 1 PPB making it hard to distinguish between the two lesions. Also, CPAM type 1 has been associated with bronchioloalveolar carcinoma in both pediatric and adult cases.1

Bronchopulmonary Sequestrations

BPS is a mass of pulmonary tissue that is typically cystic in nature, although it may be solid. It does not communicate with the tracheobronchial tree. BPS has its own blood supply arising from the systemic arterial system, rather than the pulmonary artery, and its venous drainage may occur via the pulmonary or systemic veins.2,13,16 There are two types of BPS, intralobar and extralobar, distinguished based on their pleural covering1 (Figure 3). The intralobar sequestration occurs within the normal anatomic lobe of the lung and does not have its own pleural covering. The extralobar sequestration maintains a complete anatomical separation from the normal lung and has its own distinct pleural covering.1,16 Most extralobar sequestrations occur in the thoracic cavity but some occur below the diaphragm.13 Most intralobar sequestrations are located in the left lower lobe, typically in the medial and posterior basal segments.13,16

Chest radiograph of a 16-month-old boy with intralobar pulmonary sequestration of the right middle lobe.

Figure 3.

Chest radiograph of a 16-month-old boy with intralobar pulmonary sequestration of the right middle lobe.

BPS is a rare malformation representing up to 6% of CLMs.13,16 Intralobar sequestrations are the most prevalent accounting for 80% to 85% of all BPSs.13,16 Both males and females are equally affected with intralobar sequestrations; however, there is a male predominance (4:1) with extralobar lesions.16 About 60% of extralobar sequestrations are associated with other congenital anomalies such as CDH, CPAM, CLE, and/or cardiac malformations.13,16

The etiology of BPS remains a much-debated topic. The predominant theory is that they are an embryologic anomaly derived from an accessory lung bud that forms during fetal development.13,16 This theory posits that during early development there is the creation of an accessory foregut bud that forms an additional structure in parallel to normal lung development. If this bud forms early, it is typically found within the normal lung tissue forming an intralobar sequestration. If this accessory bud forms later in embryologic development, an extralobar sequestration is created outside the lung.16

The majority of BPS are identified during prenatal imaging. Some lesions may appear to regress during the prenatal course; however, all infants require postnatal imaging to be certain. Most infants with extralobar sequestrations will present with respiratory distress within the first 6 months of life, with about 25% presenting at birth. Infants may also present with chronic cough, recurrent pulmonary infections, difficulty feeding, and/or abdominal pain.13 Intralobar sequestrations, if not detected prenatally, typically present later in childhood (older than age 2 years) with chronic pneumonia.13,16

It is important to clearly identify the BPS location and its blood supply.13 CT, MRI, and Doppler ultrasound are most often used, each with its unique advantages and disadvantages. CT imaging best demonstrates the lung parenchyma but may not be as useful in mapping the blood supply. MRI imaging has the advantage of being able to map the blood supply with no radiation exposure but requires sedation.13 Doppler ultrasound can map arterial and venous blood supply but is not a great modality for viewing surrounding parenchyma. A study by Ruano et al.17 demonstrated that the use of three-dimensional Doppler ultrasound reliably differentiated BPS from CPAM along with identifying the feeding vessels.13

There is often overlap between BPS and CPAM in what are now called hybrid lesions.1,2 These hybrid malformations have coexisting features of both pulmonary sequestration and CPAM. In one case series, Conran and Stocker18 found that one-half of the patients with extralobar sequestration (23 of 46) had a coexistent CPAM type 2 based on histology.

Congenital Lobar Emphysema

CLE is the overinflation, or hyperinflation, of one or more pulmonary lobes causing compression of the surrounding structures.2,13,19 This lesion occurs secondary to focal airway collapse on expiration resulting in air trapping, which in turn causes focal overdistention and emphysematous changes.2 About one-half of CLE lesions are located in the left upper lobe, whereas the right upper lobe and middle lobe involvement are less frequently noted1 (Figure 4 and Figure 5).

Chest computed tomography of a 2-day-old with congenital lobar emphysema of the left upper lobe (coronal view).

Figure 4.

Chest computed tomography of a 2-day-old with congenital lobar emphysema of the left upper lobe (coronal view).

Chest computed tomography of a 2-day-old with congenital lobar emphysema of the left upper lobe (axial view).

Figure 5.

Chest computed tomography of a 2-day-old with congenital lobar emphysema of the left upper lobe (axial view).

The etiology of CLE is idiopathic in about 50% of cases. The other one-half of cases are subdivided into intrinsic or extrinsic causes.13,19 Intrinsic causes include, but are not limited to, dysplasia or deficient bronchial cartilage, bronchomalacia, impacted mucus, excessive mucosal proliferation, bronchial atresia, and bronchial torsion. Extrinsic causes include lesions or anomalies that compress the bronchi, such as cardiopulmonary vessels, cysts, and mediastinal tumors.13,19

Approximately one-quarter of cases of CLE are symptomatic at birth with respiratory distress, tension pneumothorax, and/or focal wheezing. Many patients become symptomatic within the first 6 months of life.2 However, patients may remain asymptomatic depending on size of lesion.13,19 Postnatal testing should include chest radiograph, echocardiogram, and CT or MRI scan. Note that CLE can appear similar to both a simple and tension pneumothorax on chest radiograph. The prognosis for CLE is typically excellent because hyperinflation is often reversible with surgical resection and there is no known association with malignancies.19

Bronchogenic Cysts

Bronchogenic cysts are typically unilocular, singular cysts filled with mucus or fluid and lined with pseudostratified ciliated columnar respiratory epithelium. Cysts may contain cartilage, mucous glands, and/or smooth muscle in their walls.13,20 Typically, cysts are in the mediastinum, either in the right paratracheal or carinal region, but may also be intrapulmonary. Some mediastinal cysts may communicate with the tracheobronchial tree; however, if the cysts are intrapulmonary, there is no communication.1,17

If not detected by prenatal ultrasound, the clinical presentation is variable in symptoms and timing based on the location and size of the lesion.20 Most symptomatic cysts present in infancy or early childhood with recurrent secondary infection, cough, wheeze, respiratory distress from airway compression, or pulmonary hemorrhage.1,20 However, up to 20% of cases of bronchogenic cysts remain asymptomatic and are only detected as an incidental finding on chest radiograph.20

Radiographic findings vary from a smooth, round mediastinal mass to a hyperinflated or atelectatic lobe of lung similar in appearance to CLE.1,20 When a bronchogenic cyst is suspected, a CT or MRI scan is recommended to better define the anatomy. It is important to note that once a bronchogenic cyst becomes complicated with infection or bleeding it is harder to differentiate from other lung lesions, such as abscess, pulmonary mass, sequestration, or metastasis.13

Bronchogenic cysts are at increased risk for malignant transformation.2 Although rare, there have been multiple case reports of rhabdomyosarcoma, pulmonary blastoma, bronchopulmonary carcinoma, and malignant mesenchymoma found in resected bronchogenic cysts in both children and adults.13

Management of CLMs

There is a unanimous consensus that if a CLM is symptomatic, it should be surgically resected.1,2,7,8,13 However, the management of asymptomatic children with prenatally diagnosed or incidentally found CLMs is the cause of much debate. The support for universal elective surgical resection of asymptomatic lesions is based largely on preventing future complications including infection, malignancy, pneumothorax, and allowing for optimal lung growth. Studies have shown surgical complication rates are low, ranging from 6% to 9%,8 consisting mainly of postoperative air leaks. The mortality rate is nearly zero when surgery is performed by an experienced surgeon.8 Two small prospective studies demonstrated that most infants who had resection of lesions in infancy had normal pulmonary function at follow up.8 The timing of the surgery also remains controversial with those in favor of early intervention arguing that the risk of infection or other complications will only make surgical resection more difficult. Most institutions will delay surgery until at least age 2 to 3 months to decrease anesthetic risk.8

The case for expectant management (watchful waiting) is based on the idea that the natural history of these lesions is not known with any certainty and the majority of patients will remain asymptomatic throughout their lifetime; therefore, not justifying the surgical risks.7,21 Recent studies from the United Kingdom suggest that only 3% to 9% of cases with initially asymptomatic lesions develop symptoms, with no symptomatic development after age 10 years.7,10 The authors in support of expectant management note the disparity between the prevalence of CLMs and the observed incidence of malignant lung tumors in children. They argue that the prevalence of CLMs and actual observed incidence of malignancy are so different that CLMs cannot be a premalignant lesion and therefore do not need elective resection.1,7

Congenital Pulmonary Airway Malformations

Most clinicians advocate for elective resection via video-assisted thoracoscopic surgery (VATs) or thoracotomy of an asymptomatic CPAM due to the increased risk of recurrent infections and other complications, particularly its known association with bronchoalveolar carcinoma, PPB, and rhabdomyosarcoma.1 Currently no imaging modality can reliably distinguish between the appearance of a malignant lesion and a CPAM. Even histopathologically, there have been reported problems differentiating between a CPAM type 4 and PPB type 1.8 The recommended timing, although still controversial, appears to be between ages 3 and 6 months.1,8

Bronchopulmonary Sequestration

Most authors recommend surgical resection via VATs or thoracotomy of asymptomatic pulmonary sequestrations due to the risks of infection, hemorrhage, and/or malignant transformation. They are particularly concerned with intralobar and subdiaphragmatic pulmonary sequestrations as they may represent malignancy.1 Some authors make the argument for expectant management for extralobar sequestrations as they are at lower risk of developing complications.1

Cho et al.22 has also demonstrated successful regression of pulmonary sequestration when treated by arterial embolization occluding feeding vessels to the sequestration postnatally. Although this is a promising new intervention, one must keep in mind that this is a relatively new treatment modality with only a few case series in the literature.1

Congenital Lobar Emphysema

Management for CLE is mainly focused on treating the underlying cause of lobar hyperinflation if a patient is symptomatic. However, surgical resection of an asymptomatic, or even mildly symptomatic patient with CLE is not always necessary.19 Most authors agree that conservative expectant management may be justified in these lesions because patients have a lower risk of future complications and malignancy as compared to other CLMs.1

Bronchogenic Cyst

Many asymptomatic cysts are excised via VATs or thoracotomy due to their risk of expansion causing airway obstruction, infection, hemorrhage, and malignant transformation.2,13,20 Resection can typically occur without significant loss of adjacent lung tissue.2

Conclusion

CLMs comprise a spectrum of anatomical anomalies of the lungs and respiratory tree.1,2 Overall, the prenatal growth pattern of CLMs is unpredictable with larger lesions causing life-threatening complications, such as hydrops fetalis, and smaller lesions remaining asymptomatic and potentially regressing.1,7 An abnormal prenatal ultrasound is the most common presentation of CLMs in the US and Europe.10 The most common CLMs are CPAM, BPS, CLE, and bronchogenic cysts. These lesions have clinically similar presentations, when symptomatic, but each has pathophysiologic differences to consider when evaluating and treating.

Postnatal evaluation is required for all infants found to have prenatal CLM, even if asymptomatic or appearing to have possibly regressed on ultrasound. Every patient with a CLM who becomes symptomatic requires surgical resection of the lesion either via VATs or thoracotomy. The best postnatal management of an asymptomatic CLM remains unclear. Some clinicians recommend close monitoring of patients, especially with CLE or extralobar pulmonary sequestrations. Others advocate for the elective resection of CPAMs, intralobar pulmonary sequestrations, and bronchogenic cysts.1 Most clinicians agree that postponing surgery in asymptomatic children until age 3 to 6 months appears safe without increasing the risk of postoperative complications or long-term impairment of pulmonary function.8 Controversary regarding the management of CLMs will continue until long-term prospective studies of prenatally diagnosed asymptomatic CLMs are done and the natural history of these lesions are elucidated.

References

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  15. Calvert JK, Lakhoo K. Antenatally suspected congenital cystic adenomatoid malformation of the lung: postnatal investigation and timing of surgery. J Pediatr Surg. 2007;42:411–414. doi:. doi:10.1016/j.jpedsurg.2006.10.015 [CrossRef]
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Congenital Pulmonary Adenomatoid Malformations Classification

Type Origin Description
0 Tracheal and/or bronchial Rare, associated with other abnormalities, incompatible with life
1 Bronchial and/or bronchiolar Consists of large cysts, single or multiloculated; cysts from 2–10 cm in diameter; most common type of CPAM; best prognosis
2 Bronchiolar Consists of small cysts (single or multiple); cysts from 0.5–2 cm in diameter; second most common type of CPAM; up to 60% of cases associated with other anomalies
3 Bronchiolar and/or alveolar duct Adenomatoid lesion with microcystic appearance; cysts <0.5 cm in diameter; relatively uncommon type of CPAM; may appear as a solid mass on imaging because so small; typically involves whole lobe with compression of the adjacent lung parenchyma; near absence of pulmonary arteries within the lesion
4 Distal acinar Consists of multiloculated large cysts; it is an uncommon type of CPAM

CPAM Prenatal Screening Classification

Type Description
1 Macrocystic: cysts >5 mm in size
2 Microcystic: cysts <5 mm in size (appear solid on ultrasound)
Authors

John Palla, MD, is a Pediatric Pulmonary Fellow, Baylor College of Medicine, Texas Children's Hospital. Marianna M. Sockrider, MD, DrPH, is an Associate Professor of Pediatric Pulmonary Medicine, Baylor College of Medicine; and the Chief of Pulmonary Clinics, Texas Children's Hospital.

Address correspondence to John Palla, MD, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030; email: john.palla@bcm.edu.

Disclosure: The authors have no relevant financial relationships to disclose.

10.3928/19382359-20190326-02

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