Congenital pulmonary airway malformation (CPAM), formerly known as Congenital Cystic Adenomatoid Malformation (CCAM), is a rare, non-cancerous developmental anomaly of the fetal lung. This condition involves the growth of abnormal, non-functional lung tissue that presents as a mass or a collection of cysts in the baby’s chest. CPAM is typically identified during a routine prenatal ultrasound, leading to close monitoring throughout the pregnancy and specialized care after birth. The prognosis for most children is very favorable, especially with timely medical and surgical management.
Defining Congenital Pulmonary Airway Malformation (CPAM)
CPAM is characterized by an overgrowth of disorganized tissue from the distal airways, such as the bronchioles. This congenital malformation results in the formation of cysts or a solid-appearing mass, generally affecting only one lobe of a single lung. The abnormal tissue stems from a disturbance in the normal branching and maturation of the bronchial tree during early fetal development.
The medical community transitioned from the older term CCAM to CPAM because the former was imprecise; not all lesions are cystic, and “adenomatoid” only described one subtype. CPAM is a broader term for the spectrum of airway malformations. The underlying cause of this developmental error remains unknown, but it is not typically genetic, inherited, or related to maternal actions during pregnancy.
The abnormal lung tissue does not participate in gas exchange. The mass can cause a “mass effect” by pushing on healthy lung tissue, the heart, and major blood vessels in the chest. This compression can impair the development of the remaining healthy lung tissue and interfere with cardiac function. The nature of the mass, whether large cysts or tiny cysts, determines its classification and potential risk to the fetus.
Detection and Severity Classification
CPAM is most often detected during a routine second-trimester fetal ultrasound, typically around 18 to 20 weeks of gestation. The lesion appears as an echogenic, or bright, mass, ranging from a single large cyst to a solid-looking mass composed of many microcysts. Fetal Magnetic Resonance Imaging (MRI) is often used after the initial ultrasound to confirm the diagnosis and provide a detailed anatomical assessment of the lesion and its effect on surrounding structures.
Severity is commonly classified using the Stocker system, which categorizes the malformation into five types (Type 0 through Type 4). Classification is based on the size of the cysts and the presumed origin of the abnormal tissue. Type 1 lesions, the most common, contain one or more large cysts. Type 2 lesions have medium-sized cysts, and Type 3 lesions are composed of microcysts, giving them a solid appearance on imaging. This classification helps medical teams determine the probable course of the condition.
The most important metric for predicting risk during pregnancy is the Congenital Pulmonary Airway Malformation Volume Ratio (CVR). The CVR is calculated by dividing the estimated volume of the CPAM mass by the baby’s head circumference, normalizing the lesion size for gestational age. Physicians use a CVR of 1.6 as a threshold to predict a high risk for hydrops fetalis. Hydrops fetalis is a severe condition involving abnormal fluid accumulation in two or more fetal body compartments. Lesions with a CVR above 1.6 significantly increase the risk of hydrops, prompting closer monitoring or prenatal intervention planning.
Management and Treatment Options
Management for CPAM follows one of three primary pathways, determined by the lesion’s size, classification, and fetal complications. For the majority of cases, where the lesion is small or the CVR is low, the baby is managed with expectant monitoring. This involves frequent prenatal ultrasounds to track the lesion’s size. Many CPAM lesions decrease in size or appear to resolve, known as “vanishing CPAM,” as the pregnancy progresses. Delivery is typically planned at term in a facility equipped with a specialized neonatal intensive care unit.
Prenatal intervention is reserved for the small percentage of large lesions causing severe complications, particularly hydrops fetalis. For macrocystic lesions (Type 1), a thoracoamniotic shunt may be placed to drain fluid from the cyst into the amniotic cavity, relieving pressure on the fetal heart and lungs. For microcystic lesions with hydrops, maternal administration of steroids, such as betamethasone, can sometimes reduce the size of the mass and reverse the hydrops.
Postnatal treatment for CPAM, even in asymptomatic infants, almost always involves elective surgical resection of the abnormal lung lobe. This procedure, called a lobectomy, is generally performed between one and six months after birth, often using minimally invasive thoracoscopic techniques. Surgery is recommended for asymptomatic babies primarily to prevent two future complications. The first is recurrent lung infections, as the abnormal tissue is prone to developing pneumonia. The second is the small risk of malignant transformation into certain types of lung cancer, such as pleuropulmonary blastoma.
Prognosis and Long-Term Monitoring
The long-term prognosis for babies diagnosed with CPAM is overwhelmingly positive, particularly after successful surgical removal of the lesion. Following a lobectomy, the remaining healthy lung tissue has a remarkable capacity for compensatory growth, often expanding to fill the space left by the removed lobe. This growth potential is highest during infancy and early childhood, which is a major reason for performing the elective surgery early in life.
Most children who have their CPAM resected lead normal, active lives with little long-term impairment in respiratory function. Long-term follow-up care is necessary to ensure the child’s continued well-being. Monitoring includes periodic physical exams and imaging studies, such as chest X-rays or CT scans, to assess the compensatory growth of the remaining lung and monitor the surgical site. Even if the lesion appeared to resolve before birth, a postnatal CT scan is often recommended because abnormal tissue may still be present, posing a risk for later infection.