Congenital pulmonary airway malformation (CPAM), previously known as cystic adenomatoid malformation (CCAM) of the lung is a multicystic mass of abnormally developed lung tissue. The condition occurs sporadically in approximately 1:8,000-1:35,000 births. The lesion results from an overgrowth of terminal respiratory bronchioles that form cysts of various diameters and can be diagnosed antenatally with ultrasound. The lesion communicates with the tracheobronchial tree. Postnatally, CPAM is classified into five types (0, 1, 2, 3, and 4) based on surgical pathology analysis. Antenatally, the lesion is classified based on the ultrasound appearance into 3 classic types, using roman numerals: Type I (macrocystic) is comprised of cysts that measure between 2 and 10 centimeters in diameter. Type II (macrocystic with microcystic component) have cysts less than 2 centimeters is diameter. Type III (microcystic) have cysts that measure less than 0.5 centimeters in diameter, and appear solid and echogenic on prenatal ultrasound. The cysts themselves are not distinguishable by ultrasound in Type III. CPAM may affect one or both lungs. Congenital Lobar Emphysema (CLE) is a congenital disorder in which the lung becomes hyperinflated. In utero, it may appear indistinguishable from a microcystic type III CPAM.

CPAM may affect fetal outcome in one of several ways:

• By compromising growth and development of the normal lung tissue due to a space-occupying effect
• By compromising venous or lymphatic return to the heart, resulting in hydrops
• By causing esophageal compression and polyhydramnios, with increased risk for preterm labor and delivery.

Fetal or neonatal demise may result from any of the above mechanisms. Rarely, CPAM may also result in malignant transformation.

Antenatally, CPAMs may show a variable behavior. Up to 50% of lesions are thought to either decrease or disappear altogether. Because a histological diagnosis is not available in these cases, it is not possible to state whether all resolving lesions represent CPAMs. Lesions may also increase in size and compromise lung development or result in hydrops. Genetic testing is usually not indicated, given the sporadic nature of the lesion.

The antenatal management of CPAM depends on whether fetal compromise is evident of suspected. Fetuses with hydrops have the worse prognosis. Large cysts (type I) may be successfully treated with a thoracoamniotic shunt. The decision to offer treatment is based both on the size of the cyst as well as on the compromise to lung development. Type III lesions associated with hydrops have been successfully treated with percutaneous fetal sclerosis. The use of antenatal corticosteroids has also been proposed as a non-invasive method of treatment, but results vary.