Chin and Tang first described cystic adenomatoid malformation (CAM) as a distinct entity in 1949. 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.
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.
1977, Stocker grossly classified CCAM into 3 types based mostly on cyst size.
1977, Stocker grossly classified CCAM into 3 types based mostly on cyst size.
- Type I includes multiple large cysts (>2 cm in diameter) or a single large cyst surrounded by numerous smaller cysts. Type I is the most common type of CCAM and is associated with an excellent prognosis.
- Type II CCAM has multiple small cysts, usually less than 1 cm in diameter, and accounts for over 40% of cases of CCAM. In Stocker\'s series, as many as 60% of type 2 lesions are associated with other congenital anomalies that may affect prognosis, specifically renal agenesis.
- Type III CCAMs are large and account for less than 5% of all cases. They consist of multiple microcysts, measuring less than 0.5 cm in diameter.
- In 1993, Adzick reported his group system of classification. Microcystic lesions (cysts measuring <5 mm) were usually associated with fetal hydrops and, hence, a poor prognosis. Macrocystic lesions (ie, cysts >5 mm) were not usually associated with hydrops and had a good prognosis.
CAM is differentiated from other congenital cystic disease by 5 characteristics:
- 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.
Radiographic 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.
DIFFERENTIALS
1. Pneumatoceles that form subsequent to bacterial pneumonia (eg, streptococcal, staphylococcal) can be mistaken for CAM, particularly in the older child.
2. 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.
3.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.
4.On plain radiographs, intrapulmonary sequestration with infection and abscess formation can be difficult to differentiate from CAM .
CT findings
- 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.