Imaging in Congenital Cystic Adenomatoid Malformation

Updated: Jun 30, 2016
  • Author: Gerald Mandell, MD, FACR, FAAP, FACNM; Chief Editor: John Karani, MBBS, FRCR  more...
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Overview

Overview

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. Stocker in 2002 recommended the term congenital pulmonary airway malformation (CPAM) as being preferable to the term congenital cystic adenomatoid malformation, since the lesions are cystic in only 3 of the 5 types of these lesions and are adenomatoid in only 1 type (type 3). [2]

The following 2 radiographs are from the same infant with congenital cystic adenomatoid malformation:

Initial anteroposterior radiograph of the chest in 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.
On the second day of life (same patient as in prev On the second day of life (same patient as in previous image), 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.

Types of CAM

CAM is subdivided into 3 major types [3] :

  • 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. [4]

Differential diagnosis

CAM is differentiated from other congenital cystic disease by 5 characteristics [5, 6, 7] :

  • 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

Preferred examination

CAM may be initially detected during prenatal ultrasonography. [8] After birth, chest radiography should be performed first. [9] 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. [10, 11, 12, 13, 14]

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.

In a retrospective study, Scialpi et al proposed that because of similar CT scan patterns between intrapulmonary bronchogenic cyst (IBC) and type I CAM that precluded differentiation, surgical resection of all intrapulmonary cystic lesions in adults is required, as type I CAM is a precursor of mucinous bronchioloalveolar carcinoma. [15] In the study, of 9 patients with a histologic diagnosis of pulmonary cystic disease following surgery, 6 had IBC and 3 had type I cystic adenomatoid malformation (CAM). (See the CT Scan discussion below.)

Komori et al determined the optimal age for surgery in patients with congenital cystic lung disease is younger than 1 year. They used radionuclide imaging to assess long-term pulmonary function following lobectomy for congenital cystic lung disease in 93 infants and children. Patients who were younger than 1 year at surgery had a significantly lower mean transit time (marker for air trapping) at 5 years and 10 years postoperatively than those who were older than 1 year at surgery. Additionally, at 10 years after surgery, perfusion scintigraphy scores were higher and mean transit times were lower in patients without infection compared with patients with infection. [16]

In a French study, Zeidan et al showed that prenatal MRI was less accurate than postnatal CT scan, which, according to the authors, remains the most reliable diagnostic modality to specify the location, extent, and type of lesions. [9] The authors evaluated the accuracy of prenatal MRI and postnatal CT imaging in identifying congenital cystic adenomatoid malformation and bronchopulmonary sequestration by comparison with histologic analysis. (See the CT Scan and MRI discussions below.)

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Radiography

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. Findings are usually apparent in a symptomatic individual, but they may not be as apparent in an asymptomatic child.

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, one large cyst may overshadow the others.

Air-trapping within cystic spaces can cause rapid enlargement of the CAM and subsequent respiratory embarrassment.

See the radiographic images of cystic adenomatoid malformation (CAM), below.

Initial anteroposterior radiograph of the chest in 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.
On the second day of life (same patient as in prev On the second day of life (same patient as in previous image), 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.
Anteroposterior radiograph of a patient with conge 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.

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 for 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.

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. 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. 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.

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

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Computed Tomography

CT findings are correlated with the pathologic findings. [17, 18, 19]

  • 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.

See the CT images of cystic adenomatoid malformation (CAM) below.

CT scan of the chest demonstrating a multiseptated CT scan of the chest demonstrating a multiseptated cystic lesion in the right upper lobe consistent with localized congenital cystic adenomatoid malformation.
CT image of the bases of the lungs showing an unus CT image of the bases of the lungs showing an unusual bilateral congenital cystic adenomatoid malformation.

 

Approximately 25% of lesions diagnosed as CAM may be either pulmonary sequestration or bronchogenic cysts. Overlapping CT features can also exist among other foregut malformations.

In a retrospective study, Scialpi et al proposed that because of similar CT scan patterns between intrapulmonary bronchogenic cyst (IBC) and type I CAM that precluded differentiation, surgical resection of all intrapulmonary cystic lesions in adults is required, as type I CAM is a precursor of mucinous bronchioloalveolar carcinoma. [15] In the study, of 9 patients with a histologic diagnosis of pulmonary cystic disease following surgery, 6 had IBC and 3 had type I CAM.

In a French study, Zeidan et al showed that prenatal MRI was less accurate than postnatal CT scan, which, according to the authors, remains the most reliable diagnostic modality to specify the location, extent, and type of lesions. [9] The authors evaluated the accuracy of prenatal MRI and postnatal CT imaging in identifying congenital cystic adenomatoid malformation and bronchopulmonary sequestration by comparison with histologic analysis.

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Magnetic Resonance Imaging

In congenital cystic adenomatoid malformation (CAM), prenatal MRI findings on T2-weighted images have been reported, [20, 21, 22] such as the following:

  • 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

In a French study, Zeidan et al showed that prenatal MRI was less accurate than postnatal CT scan (see the CT Scan discussion), which, according to the authors, remains the most reliable diagnostic modality to specify the location, extent, and type of lesions. [9] The authors evaluated the accuracy of prenatal MRI and postnatal CT imaging in identifying congenital cystic adenomatoid malformation and bronchopulmonary sequestration by comparison with histologic analysis.

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Ultrasonography

Prenatal sonography enables the identification of cystic adenomatoid malformation (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

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-positive findings include bronchogenic cysts and pulmonary sequestration.

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Nuclear Imaging

Komori et al used radionuclide imaging to assess long-term pulmonary function following lobectomy for congenital cystic lung disease in 93 infants and children, and they determined the optimal age for surgery in patients with congenital cystic lung disease is younger than 1 year.

Patients who were younger than 1 year at surgery had a significantly lower mean transit time (marker for air trapping) at 5 years and 10 years postoperatively than those who were older than 1 year at surgery.

Additionally, at 10 years after surgery, perfusion scintigraphy scores were higher and mean transit times were lower in patients without infection compared with patients with infection. [16]

Previous