Diagnosis: Congenital Pulmonary Airway Malformation (CPAM/CCAM)
A fetal lung containing numerous cystic spaces at 32 weeks gestation is most consistent with congenital pulmonary airway malformation (CPAM), previously termed congenital cystic adenomatoid malformation (CCAM), which represents a developmental abnormality of the terminal bronchioles characterized by cystic or adenomatous lesions. 1, 2
Immediate Diagnostic Confirmation
Perform detailed transabdominal ultrasound to fully characterize the lesion, assess for mediastinal shift, evaluate the contralateral lung compression, measure amniotic fluid volume, and calculate the CPAM volume ratio (CVR) using the formula for a prolate ellipse divided by head circumference 1, 3
Assess for hydrops fetalis immediately, as this is the single most critical prognostic factor—all cases with nonimmune fetal hydrops have resulted in fetal death in reported series 4
Evaluate for polyhydramnios, which along with mass size and mediastinal shift determines severity 2
Risk Stratification at 32 Weeks
CVR measurement is essential for predicting neonatal respiratory outcomes:
CVR <0.5 predicts normal respiratory function with 100% sensitivity, 85.7% specificity, and 100% negative predictive value for regular nursery care 3
CVR measurements typically peak at 32 weeks and then decrease; cases requiring NICU admission show larger decreases in CVR beyond 32 weeks (p=0.002) 3
If CVR ≥0.5 at this gestational age, plan for delivery at a tertiary center with immediate NICU and pediatric surgery availability 3
Additional Imaging Considerations
Consider fetal MRI if ultrasound findings are incomplete or additional anatomic detail is needed for delivery planning, particularly for airway management planning, as MRI is especially helpful for thoracic anomalies and airway management in fetuses with masses 1
MRI should ideally be performed at or after 22 weeks gestation, making it appropriate at 32 weeks 1
Surveillance Protocol Through Delivery
Perform serial ultrasounds weekly or biweekly to monitor for development of hydrops, changes in mass size, mediastinal shift, and amniotic fluid volume 1, 2
Monitor for fetoplacental circulation disorders, which can develop in the third trimester 2
Note that approximately 9 out of 50 large pulmonary lesions may dramatically decrease in size or disappear completely during fetal life, so serial imaging is critical 5
Delivery Planning
Delivery should occur at a tertiary care center with immediate access to:
- Neonatal intensive care unit
- Pediatric surgery capability
- Respiratory support including mechanical ventilation 2, 6
Timing of delivery:
If hydrops develops, immediate delivery is indicated regardless of gestational age (though prognosis is dismal) 4
If stable without hydrops and CVR <0.5, delivery can proceed at term with standard obstetric indications 3
If CVR ≥0.5 or signs of fetal compromise, consider delivery at 36-37 weeks after administration of corticosteroids for lung maturation 2
Genetic Counseling
Perform amniocentesis and karyotype identification, though chromosomal anomalies are rarely identified in association with CPAM 2
Detailed anatomic survey should be performed to identify any additional structural anomalies 1
Postnatal Management Expectations
Immediate neonatal care may include:
Antibiotics, caffeine citrate, and respiratory support 2
CT scan is the most reliable imaging method for confirming diagnosis postnatally 2
Surgical resection (segmentectomy or lobectomy) is safe with low complication rates and excellent results 6
Even without immediate symptoms, surgical excision is generally recommended due to risk of infection, pneumothorax, and rare malignant transformation 6
Critical Pitfall to Avoid
Do not assume a poor prognosis based solely on initial mass size at 32 weeks—the natural history is highly variable, and marked improvement can occur during fetal life if hydrops is absent 5. However, the presence of hydrops fetalis is an absolute negative predictor requiring immediate intervention 4.