AUTHOR AND EDITOR INFORMATION

Section 1 of 10  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• MRI
• Ultrasound
• Intervention
• Multimedia
• References

INTRODUCTION

Section 2 of 10  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• MRI
• Ultrasound
• Intervention
• Multimedia
• References

Background

Ch'in and Tang first described cystic adenomatoid malformation (CAM) as a distinct entity in 1949.¹ CAM is a developmental hamartomatous abnormality of the lung, with adenomatoid proliferation of cysts resembling bronchioles. CAM represents approximately 25% of all congenital lung lesions.

Pathophysiology

Pathogenesis and pathophysiologic features

CAM is believed to result from focal arrest in fetal lung development before the seventh week of gestation secondary to a variety of pulmonary insults. Depending on the time and type of insult, 4-26% of cases can be associated with other congenital abnormalities. However, arrest of pulmonary development with distortion of architectural differentiation may take place at any stage of embryonic development.

CAM differs from normal lung tissue because of a combination of increased cell proliferation and decreased apoptosis. A well-defined intrapulmonary bronchial system is lacking, and normally formed bronchi supplying the mass are absent.

Types of CAM

CAM is subdivided into 3 major types²:

• Type I lesions, the most common, are composed of 1 or more cysts measuring 2-10 cm in diameter. Larger cysts are often accompanied by smaller cysts, and their walls contain muscle, elastic, or fibrous tissue. Cysts are frequently lined by pseudostratified columnar epithelial cells, which occasionally produce mucin. Mucinogenic differentiation is unique to this subtype of CAM.
• Type II lesions are characterized by small, relatively uniform cysts resembling bronchioles. These cysts are lined by cuboid-to-columnar epithelium and have a thin fibromuscular wall. The cysts generally measure 0.5-2 cm in diameter.
• Type III lesions consist of microscopic, adenomatoid cysts and are grossly a solid mass without obvious cyst formation. Microscopic adenomatoid cysts are present.

CAM receives its blood supply from the pulmonary circulation and is not sequestered from the tracheobronchial tree. However, type II and III lesions can occasionally coexist with extralobar sequestration, and in such cases, they may receive systemic arterial supply. CAM may also occur in combination with a polyalveolar lobe. A polyalveolar lobe is a form of congenital emphysema with increased number of alveoli with normal bronchi and pulmonary vasculature. CAM usually occurs early in fetal life, whereas polyalveolar lobe occurs late.

Differential diagnosis

CAM is differentiated from other congenital cystic disease by 5 characteristics³:

 

• Absence of bronchial cartilage (unless it is trapped within the lesion) 
• Absence of bronchial tubular glands
• Presence of tall columnar mucinous epithelium
• Overproduction of terminal bronchiolar structures without alveolar differentiation, except in the subpleural areas
• Massive enlargement of the affected lobe that displaces other thoracic structures

Frequency

International

In Canada, the estimated incidence of CAM is 1 case per 25,000-35,000 pregnancies⁴.

Mortality/Morbidity

The prognosis primarily depends on the size of the lesion. In a Canadian series of 48 patients, the incidence of postnatal demise was 10% (10 of 40 patients) with 8 spontaneous and voluntary abortions.⁴ Larger lesions have a higher incidence of mediastinal shift, vascular compromise, polyhydramnios, pulmonary hypoplasia, and hydrops, which may lead to intrauterine fetal demise or neonatal death (see Polyhydramnios, Pulmonary Hypoplasia, and Hydrops Fetalis). 

Type III CAM tends to be extensive and therefore tends to have a poor prognosis. The prognosis is also poor with bilateral lung involvement, prematurity, and severe associated malformations. The most commonly associated anomalies occur in the type II form. The anomalies affect the renal (cystic disease, agenesis, dysgenesis), intestinal (atresias), cardiac, and osseous systems.

• When CAM is identified in utero, as many as 56% of the lesions detected can regress spontaneously, although they may initially progress. As the lesion decreases in size, mediastinal shift is corrected. Persistent lesions may only be discovered later in life, and some may be asymptomatic. Eventual removal of even asymptomatic masses is recommended because of potential risk of secondary infection and hemorrhage and because of reports of carcinomas arising in CAM.
• In fetuses with life-threatening lesions, such as the development of hydrops, the anticipated mortality is nearly 100%.

Race

No clear racial predilection for CAM exists.

Sex

Sex-related incidences are equal for CAM.

Age

Most cases of CAM are diagnosed in the patient's first 6 months of life, with 70% of patients presenting in the first month of life. As many as 90% of cases are reported within the patient's first 2 years of life. Occasionally, CAM is discovered later in life, usually as a result of chronic or recurrent pulmonary infection.

When CAM was diagnosed prenatally in one study, the mean gestational age at diagnosis was 22.6 weeks ± 3.3.

Anatomy

Communication with the tracheobronchial tree usually is retained, and the vascular supply and venous drainage are to the pulmonary circulation, unless CAM is associated with sequestration, as discussed above. Lesions occur with equal frequency in the lungs, but the lesions have a slight predilection for the upper lobes. Lobar involvement is seen most often, but multiple lobes, the entire lung, or segments of both lungs may be involved.

Clinical Details

In the newborn, 80% of cases of CAM present with some degree of respiratory distress secondary to mass effect and pulmonary compression or hypoplasia. Severe symptoms may be related to air trapping within the lesions. The affected region is dull to percussion, and air entry is poor. Older patients may present with persistent or recurrent pneumonia.

Preferred Examination

CAM may be initially detected during prenatal ultrasonography. After birth, chest radiography should be performed first. Although lesions remain filled with fluid, postnatal sonography can be used for a more detailed assessment, particularly in type III lesions. Once lesions are air-filled, CT scanning is necessary for determination of the type and extent of the lesions.

Limitations of Techniques

Prenatal ultrasonography is accurate in diagnosing CAM. Prenatally diagnosed lesions may be asymptomatic at birth (71%), and they have normal radiographic findings (57%). A concurrent sequestration may not be identified. Usually, radiographic findings are apparent in a symptomatic individual, but they may not be as apparent in an asymptomatic child.

Most often, the diagnosis can be made by using plain radiographs. CT scans may be used to diagnose confusing cases. Overlapping CT features exist among cases of CAM, pulmonary sequestration, bronchogenic cyst, and other foregut malformations. CT is more accurate than radiography or ultrasonography in classifying the type of CAM.

DIFFERENTIALS

Section 3 of 10  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• MRI
• Ultrasound
• Intervention
• Multimedia
• References

Other Problems to Be Considered

Postinfectious pneumatoceles

RADIOGRAPH

Section 4 of 10  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• MRI
• Ultrasound
• Intervention
• Multimedia
• References

Findings

• Usually, the radiographic pattern appears as an expansile soft-tissue mass containing multiple air-filled cystic masses of varying size and shifting of the mediastinum.
• Initially and early in life, a homogeneous fluid-opacity pulmonary mass may present and evolve to demonstrate an air-filled cystic radiographic appearance. The initial dense appearance is a result of delayed emptying of alveolar fluid via either the bronchi or lymphatic and circulatory systems.
• In patients with CAM, the pattern in the lung demonstrates multiple radiolucent areas that vary greatly in size and shape.
• Cysts are separated from each other by strands of opaque pulmonary tissue.
• The involved lung may appear honeycombed or spongy, but occasionally, 1 large cyst may overshadow the others.
• Air-trapping within cystic spaces can cause rapid enlargement of the CAM and subsequent respiratory embarrassment.
• Findings are usually apparent in a symptomatic individual, but they may not be as apparent in an asymptomatic child.

Degree of Confidence

Most often, the diagnosis can be made by using plain radiographs. Most commonly, CAM appears as a mass composed of numerous air-containing cysts scattered irregularly throughout a segment of the lung. The mass is space occupying, expanding the ipsilateral hemithorax and shifting the mediastinum to the contralateral side. Usually, CT is not necessary to the diagnosis of CAM in the neonatal period. Identifying the lobe involved or determining the extent of mass effect on the uninvolved lung may be possible. CT can be used to diagnose confusing cases encountered in infancy, childhood, or adult life or for planning surgery.

False Positives/Negatives

Pneumatoceles that form subsequent to bacterial pneumonia (eg, streptococcal, staphylococcal) can be mistaken for CAM, particularly in the older child.

Congenital lobar emphysema refers to overexpansion of 1 lobe, typically an upper lobe or right middle lobe, that leads to mass effect and respiratory distress (see Congenital Lobar Emphysema). Although this entity could potentially be confused with CAM, typical features of overexpanded but normal parenchyma can be observed and confirmed with CT if necessary. Pulmonary interstitial emphysema may resemble CAM when it is complicated by large air collections (see Pulmonary Interstitial Emphysema). However, these are also typically associated with linear collections and preceded by high-pressure ventilation and barotrauma. The air collections are located in the interstitial lymphatics. On plain radiographs, intrapulmonary sequestration with infection and abscess formation can be difficult to differentiate from CAM (see Pulmonary Sequestration).

Bronchogenic cysts are usually fluid filled and well circumscribed (see Bronchogenic Cyst). Neuroenteric cysts are posterior mediastinal soft-tissue masses that are usually associated with vertebral anomalies.

CT SCAN

Section 5 of 10  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• MRI
• Ultrasound
• Intervention
• Multimedia
• References

Findings

CT findings are correlated with the pathologic findings.^{5, 6, 7}

• Areas of small cysts (<2 cm in diameter) appearing with other abnormalities (a larger cystic area, consolidation, or low attenuation) are the most frequent findings.
• Multiple large cystic lesions (>2 cm in diameter) are seen alone or with other abnormalities (areas of small cysts, consolidation, or low attenuation).
• Low-attenuation areas are clusters of microcysts.
• Air-fluid levels can be seen in some cysts. These lesions may be predominantly type I, type II, or a combination of both.
• CAM may completely resolve, as indicated by sonographic and plain radiographic criteria, but persistent abnormalities are well demonstrated on CT examination.

Degree of Confidence

Approximately 25% of lesions diagnosed as CAM may be either sequestration or bronchogenic cysts.

False Positives/Negatives

Overlapping CT features can exist among cases of CAM, pulmonary sequestration, bronchogenic cyst, and other foregut malformations.

MRI

Section 6 of 10  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• MRI
• Ultrasound
• Intervention
• Multimedia
• References

Findings

In CAM, prenatal MRI findings on T2-weighted images have been reported.^{8, 9}

• CAMs appear as intrapulmonary masses with increased signal intensity on T2-weighted images. Type I or type II CAM lesions have very high signal intensity almost equal to that of amniotic fluid and markedly higher than that of the surrounding unaffected lung tissue.
• With increasing numbers of microcysts or macrocysts, discrete cystic components may be seen within the mass lesion. Cysts larger than 3 mm are visualized easily.
• Type III CAM lesions have moderately high signal intensity. The signal intensity is higher than that of unaffected lung tissue but not as high as that of amniotic fluid. Type III lesions are relatively homogeneous.
• MRI may be useful to fetal surgeons for planning the surgical approach when hydrops and polyhydramnios necessitate surgical intervention.

ULTRASOUND

Section 7 of 10  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• MRI
• Ultrasound
• Intervention
• Multimedia
• References

Findings

Prenatal sonography enables the identification of CAM in a population of infants who are asymptomatic at birth. Regression of CAM on prenatal sonograms is common, but this process usually does not continue postnatally.

• Partially cystic, partially echogenic masses are characteristic of type I or type II lesions. The size or dimension of the cysts distinguishes the 2 types.
• Type III lesions may be large and entirely echogenic.
• Usually, the newborn is symptomatic at birth, with the finding of a lesion exceeding 50% of the hemithorax.

Degree of Confidence

The accuracy of prenatal ultrasonography in classifying the lesions of CAM is approximately 77%. Prenatally diagnosed lesions may be asymptomatic at birth (71%), and there may be normal findings on radiographic examinations (57%). If radiographic results are normal, CT should be performed because it is more sensitive for detection of smaller lesions.

False Positives/Negatives

False-positive findings include bronchogenic cysts and pulmonary sequestration.

INTERVENTION

Section 8 of 10  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• MRI
• Ultrasound
• Intervention
• Multimedia
• References

Treatment of CAM consists of surgical resection of the involved lobe or lobes. The postoperative response is prompt in symptomatic patients. Surgery is an option for fetuses with life-threatening lesions, such as the development of hydrops (see Hydrops Fetalis). Of such patients, who have an anticipated mortality of nearly 100%, 60% can be saved with the resection of CAM. In patients with large multicystic lesions, resection of a lobe may be performed. In fetuses with a single dominant cyst, thoracoamniotic shunts have been placed. The decision to surgically remove an asymptomatic CAM is controversial.^{10, 11}

Medical/Legal Pitfalls

• A diagnosis of CAM usually is made by using 1 or more diagnostic imaging modalities.
• Complications can occur secondary to the amount of lung involvement.
• Bilateral lung involvement may result in pulmonary dysfunction and poor outcome.
• Extirpation of all lesions may not occur if multiple segments are involved.
• A bronchopleural fistula has been described as a complication of surgery in 1 case.

MULTIMEDIA

Section 9 of 10  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• MRI
• Ultrasound
• Intervention
• Multimedia
• References

Media file 1:  Initial anteroposterior radiograph of the chest in a patient with congenital cystic adenomatoid malformation on the first day of life, with dense lungs and a suggestion that the right lung is slightly more voluminous than the left lung.
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Media type:  X-RAY

Media file 2:  On second day of life (same patient as in Image 1), an anteroposterior radiograph shows physiologic fluid resorbed from an area of congenital cystic adenomatoid malformation and replaced with an air-containing cystic area occupying the right upper lung.
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Media type:  X-RAY

Media file 3:  CT scan of the chest demonstrating a multiseptated cystic lesion in the right upper lobe consistent with localized congenital cystic adenomatoid malformation.
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Media type:  CT

Media file 4:  Anteroposterior radiograph of a patient with congenital cystic adenomatoid malformation with bilateral basilar cystic disease at several weeks of age. The patient's mediastinum is positioned toward the right, secondary to congenital scoliosis and larger left-sided cysts.
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Media type:  X-RAY

Media file 5:  CT image of the bases of the lungs showing an unusual bilateral congenital cystic adenomatoid malformation.
	View Full Size Image
Media type:  CT

REFERENCES

Section 10 of 10

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• MRI
• Ultrasound
• Intervention
• Multimedia
• References

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23. Uroz-Tristan J, Cabrera-Roca G, Wiehoff-Neumann A, et al. Bilateral and multilobar cystic adenomatoid malformation of the lung. Eur J Pediatr Surg. Dec 1998;8(6):364-7. [Medline].
24. van Leeuwen K, Teitelbaum DH, Hirschl RB, et al. Prenatal diagnosis of congenital cystic adenomatoid malformation and its postnatal presentation, surgical indications, and natural history. J Pediatr Surg. May 1999;34(5):794-8; discussion 798-9. [Medline].
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Article Last Updated: Oct 16, 2007