Congenital Pulmonary Airway Malformation

Congenital Pulmonary Airway Malformation

Marianna M. Sockrider, MD, DrPH, FAAP

Introduction/Etiology/Epidemiology

•Congenital pulmonary airway malformation (CPAM), which refers to congenital malformations of the lung, was previously known as congenital cystic adenomatoid malformations or CCAM.

•CPAMs are characterized by adenomatoid proliferation of bronchioles that results in cysts rather than alveoli. These lesions are thought to result from abnormal branching of bronchioles during lung morphogenesis. Lesions usually communicate with the normal tracheobronchial tree, though the connection may be constricted or anomalous. Blood supply is usually pulmonary arterial in origin, although some cases have been described with systemic arteries.

•CPAM has been the most commonly diagnosed lung malformation in fetuses, accounting for 30%–40% of all congenital lung diseases. Incidence is estimated at 1 in 10,000 to 1 in 35,000.

•Cases are sporadic, with no familial predisposition or known association with chromosome abnormalities. No association with race or maternal age has been found. Type 3 CPAM is seen predominantly in male infants.

Pathophysiology

•CPAM is usually unilateral, affecting only 1 lobe of the lung.

•Stocker’s classification has 5 types, based on cyst size and histopathologic findings, with proposed correspondence to insults at different levels of the airways.

—Type 0: Acinar dysplasia or dysgenesis is seen at the bronchial level and involves all lung lobes. This type is rare, incompatible with life, and associated with other abnormalities.

—Type 1: Single or multiloculated large cysts are variable in size, from 2 to 10 cm. They are seen at the bronchial and/or bronchiolar level, and this is the most common type (50%–70% prevalence) with the best prognosis. This type is localized, typically to part of 1 lobe (Figures 19-1, 19-2). There is a correlation with bronchoalveolar carcinoma.

—Type 2: Single or multiple small cysts from 0.5 to 2.0 cm occur at the bronchiolar level. This is the second most common type (15%–30% prevalence). Up to 60% of cases of type 2 CPAM occur with other associated anomalies.

—Type 3: This type has a microcystic appearance (<0.5 cm) histologically and occurs at the bronchiolar and/or alveolar duct level. It is uncommon, with 5%–10% prevalence. It involves the whole lobe, with compression of the adjacent lung. The cysts are so small that the mass may appear to be solid on images, with air spaces resembling late fetal lung and virtual absence of pulmonary arteries within the lesion histologically.

—Type 4: Multiloculated, large (≤10 cm), thin-walled peripheral cysts are seen with this type, which is uncommon (5%–15% prevalence) and has a correlation with pleuropulmonary blastoma.

•Adzick proposes only 2 categories, with detection performed via antenatal screening: macrocystic (type 1, >5 mm) and microcystic (type 2, <5 mm).

•There may be other associated abnormalities of the bronchial tree. Large lesions can compress the adjacent lung, and large cysts can cause mediastinal shift in young infants. This shift may regress with increasing age.

•There is a rare risk of neoplastic and/or malignant transformation.