In brief — the direct answer
Fetal lung lesions are abnormal masses of lung tissue that develop while the baby is in the womb. The two most common types are **CPAM** (Congenital Pulmonary Airway Malformation), which is usually cystic (fluid-filled), and **BPS** (Bronchopulmonary Sequestration), which is a solid piece of non-functioning lung tissue with its own blood supply from the aorta. While finding a 'mass' in the baby's chest is worrying for parents, the vast majority of these lesions are stable and have an excellent prognosis, with many even shrinking as the pregnancy progresses.
What is Fetal Lung Lesions (CPAM & BPS)?
Lung lesions are not cancerous. They are 'benign' overgrowths of tissue.
- CPAM: Divided into types based on the size of the cysts. Large cysts can sometimes be drained using a shunt if they are pushing on the heart.
- BPS: A 'sequestration' of lung tissue that is disconnected from the normal airway.
The main risk from these lesions is not the lesion itself, but the 'mass effect'—if the mass is large enough to push the heart to the side and compress the major veins, it can cause the baby to develop heart failure (hydrops).
Who is at risk?
Lung lesions affect approximately 1 in 2,500 to 3,000 births.
Most are isolated and occur in healthy pregnancies with no family history of lung problems. They are typically discovered during the 20-week anomaly scan when a 'bright' or 'cystic' area is seen in one of the baby's lungs.
How we diagnose it
The diagnostic goal is to assess the risk to the baby's heart:
- CVR (CPAM Volume Ratio): We measure the length, width, and height of the mass and divide it by the baby's head circumference. A CVR greater than 1.6 indicates a higher risk that the mass will cause heart strain (hydrops).
- Doppler Assessment: Using color Doppler to find the 'feeding vessel' (often coming from the aorta in BPS), which helps distinguish between different types of lesions.
- Heart Monitoring: Checking for 'mediastinal shift'—how much the heart is pushed away from its normal position.
What does management involve?
Management at the MFM Unit is individualized based on the CVR:
- Surveillance: Scans every 1-2 weeks during the peak growth period (20 to 28 weeks) to ensure the CVR is stable.
- Maternal Steroids: If the CVR is high or rising, we often give the mother a course of corticosteroids (Betamethasone). Studies show that steroids can stop the growth of CPAM and even cause it to shrink dramatically.
- Thoraco-amniotic Shunting: If a single large cyst is compressing the heart, we can place a small shunt in the womb to drain the fluid.
- Planned Delivery: Birth should take place in a tertiary center with pediatric surgeons on standby.
What are the outcomes?
The outlook for isolated lung lesions is exceptionally positive.
- Survival: Over 95% of babies with isolated CPAM/BPS survive and do well.
- Late Pregnancy: In many cases, the lesion stops growing after 28 weeks, and as the baby gets bigger, the mass becomes relatively smaller and harder to see.
- Postnatal Surgery: Some babies need a small section of their lung removed (lobectomy) after birth—either in the first weeks if they have breathing issues, or after a few months to prevent future infections. These children typically have completely normal lung function as they grow.
When to see a subspecialist
If your scan shows a 'mass in the chest' or 'bright lungs,' an immediate referral for a dedicated MFM assessment and CVR calculation is required.
Our specialists, including Dr. Ali Al-Ibrahim, provide the high-resolution imaging and the clinical expertise to monitor these lesions safely. We work in tandem with pediatric surgeons to ensure a seamless transition from prenatal monitoring to postnatal care.
Questions to ask your doctor
References & Clinical Guidelines
- ISUOG Practice Guidelines: performance of the routine mid-trimester fetal ultrasound scan
- Congenital lung malformations: antenatal and postnatal evaluation and management (consensus)
- Prenatal diagnosis and management of congenital pulmonary airway malformation