Congenital Pulmonary Airway Malformation (CPAM) is a rare, non-cancerous developmental anomaly of the lung. This condition involves the formation of an abnormal mass of non-functioning lung tissue, usually limited to one lobe of a single lung. CPAM is present at birth, arising early in gestation. While the diagnosis can be alarming, most infants with CPAM have a very positive outcome with appropriate monitoring and treatment. This article will explain the nature of this anomaly, how it is detected, and the methods used to manage it.
Defining CPAM and Its Classification
CPAM is characterized by an abnormal overgrowth of terminal airway structures, resulting in fluid-filled cysts or a solid-appearing mass within the lung tissue. This abnormal tissue cannot participate in gas exchange, occupying space needed by healthy lung tissue. The name was updated to Congenital Pulmonary Airway Malformation to reflect the spectrum of abnormalities, which are not always cystic.
The size and appearance of the malformation are classified using the Stocker system, which guides management decisions. Type I lesions are the most common (about half of all cases), consisting of one or more large cysts, each measuring more than two centimeters. Type II lesions are made up of multiple smaller cysts, generally less than two centimeters, and comprise about 40% of cases.
Type III lesions appear largely solid on imaging and have very small cysts, making up the remaining 10% of diagnoses. This classification helps professionals understand the structure of the lesion, as macrocystic (Type I) and microcystic (Type II/III) lesions can behave differently.
Prenatal Detection and Monitoring
CPAM is most often identified before birth during a routine fetal anatomy ultrasound, typically around 20 weeks of gestation. On the ultrasound, the malformation appears as an echogenic mass in the fetal chest. The size and growth of the lesion are closely monitored throughout the pregnancy to assess the potential risk to the fetus.
The primary tool for monitoring is the CPAM Volume Ratio (CVR), which normalizes the size of the lesion to the fetal head circumference. A CVR greater than 1.6 indicates an increased risk for serious complications.
A major concern is the development of hydrops fetalis, marked by fluid accumulation in the fetus’s body cavities. While the majority of CPAM cases resolve or stabilize without causing hydrops, a high CVR warns the medical team to intensify monitoring and consider specialized intervention. Postnatal imaging is still necessary, even if the lesion appears to shrink, because the tissue remains abnormal and requires management.
Treatment Approaches and Timing
The management strategy for CPAM is tailored to the individual case. For many small, asymptomatic lesions, the initial approach is expectant management, involving close observation without immediate intervention. This is often an option when the lesion remains stable or appears to regress during the pregnancy.
Fetal intervention is reserved for rare cases where the CVR is high and the fetus develops hydrops fetalis. These procedures may involve administering corticosteroids to the mother, which can help shrink microcystic lesions and reverse hydrops. For large, single-cyst lesions causing hydrops, a thoracoamniotic shunt may be placed to drain the fluid and decompress the lung.
The definitive treatment for most infants is postnatal surgery to remove the abnormal lung tissue. This is done even for asymptomatic infants because the abnormal tissue carries a risk of recurrent pulmonary infections and a small risk of malignant transformation later in life. The most common procedure is a lobectomy, which involves surgically removing the affected lobe of the lung.
The optimal timing for elective surgery on an asymptomatic infant is between three and six months of age. This window maximizes the potential for compensatory growth in the remaining lung tissue. Infants who are symptomatic at birth, experiencing respiratory distress, require immediate stabilization and may need the mass removed within the first few days or weeks of life. Complete removal of the malformation is generally curative, eliminating the risk of future complications.
Long-Term Outlook and Follow-Up Care
The prognosis for infants with CPAM is excellent. After surgical removal of the abnormal lobe, the remaining healthy lung tissue demonstrates a remarkable capacity for compensatory growth. The healthy parts of the lung expand to fill the space left by the removed lobe, often resulting in near-normal overall lung volume.
Studies show that a majority of children who undergo a lobectomy for CPAM in infancy achieve normalized lung function comparable to their peers. Follow-up care after surgery is necessary to monitor the child’s overall growth and ensure the remaining lung tissue is expanding properly. This involves periodic chest X-rays or computed tomography (CT) scans to confirm the compensatory growth and check for potential complications, such as residual cysts or scarring.