It is a rare pulmonary anomaly. It is a hamartomatous lesion characterized by a cessation of normal bronchiolar maturation, resulting in cystic overgrowth of the terminal bronchioles.

CCAM is rare and usually presents before the age of 3 years. It is more common in boys than girls, and it is usually unilateral. Patients can present with life threatening respiratory distress or a history of recurrent chest infections. Some cases are asymptomatic and are discovered as an incidental finding on radiography.

CCAM is best diagnosed with computed tomography and classified as
Type I - This is the most common type and composed of variable cysts with at least one dominant cyst greater than 2 cm. Prognosis is excellent.
Type II -Composed of smaller uniform cysts up to 2 cm. This form is commonly associated with anomalies (especially renal, cardiac, intestinal and skeletal).
Type III - Least common types and is composed of microcysts appearing solid upon visual inspection. Poor prognosis is secondary to respiratory compromise and associated congenital abnormalities.

Classification based on prenatal ultrasound findings: -
Microcystic lesions (< 5 mm): usually associated with fetal hydrops and has poor prognosis.

Macrocystic lesions (> 5 mm): not usually associated with hydrops and has favorable prognosis.

- Usually, the radiographic pattern appears as 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.

Type I lesions appear as multiple large cystic areas in the lung. In type II lesions, multiple small cysts are evident on ultrasonography. Because of the extremely small size of the cysts in type III lesions, the antenatal ultrasonographic appearance often is one of a homogenous mass. Ultrasonography may demonstrate evidence of hydrops, such as fetal ascites or pleural effusion.

Computerized chest tomography reveals the typical appearance of multilocular cystic lesions with thin walls surrounded by normal lung parenchyma; however, the presence of superimposed infection with in the lesion may complicate the appearance, resulting in air fluid levels. HRCT is sufficient to differentiate between micro cystic and macro cystic lesions.

In CAM, prenatal MRI findings on T2-weighted images have been reported

- 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.

 

Congenital lobar emphysema

Bronchogenic cyst

Bronchopulmonary sequestration,

Prior infection with pneumatocele formation

Congenital Diaphragmatic hernia.