Fetal Lung Masses: What Happens After One Is Found on Prenatal Ultrasound?

Detailed ultrasound can show us a mass’s size, location and appearance, including whether it contains cysts and how it receives its blood supply. Fetal MRI can provide additional information such as the specific lobe it is arising from, and about the mass and developing lungs.

These details help us distinguish among different types of fetal chest masses. They also help us determine whether a mass is behaving as we would expect.

That’s why a single ultrasound usually isn’t the whole story. Following the mass as the baby grows can tell us a great deal about what to expect.
 

When a baby has CPAM, we calculate a measurement called the CPAM volume ratio, or CVR, which estimates the size of the mass relative to the baby’s size.

A CVR above 1.6 has traditionally been associated with greater risk. But when that measurement occurs matters. A CVR above 1.6 when a CPAM first presents around 20 or 21 weeks can have different significance than a lesion that reaches that measurement later in pregnancy.

That’s because about 98% of CPAMs follow a predictable pattern: They reach a plateau in growth around 26 weeks and then gradually decrease in relative size. Once we see that plateau, the risk of serious problems during pregnancy becomes much lower.
 
There are exceptions, including large cystic lesions that may require closer monitoring even when the CVR initially looks reassuring. 
 

Most low-risk CPAMs have excellent outcomes and don’t require fetal treatment. 

Our concern is when a large or rapidly growing mass begins putting significant pressure on structures in the baby’s chest. In severe cases, the baby can develop hydrops fetalis, a dangerous buildup of fluid in the body.

For certain high-risk CPAMs, we may begin with corticosteroids given to the pregnant patient. If the baby doesn’t respond, fetal intervention may be considered. Today, less invasive, image-guided procedures are available for appropriately selected babies. 

The goal isn’t to treat every fetal lung mass. It’s to identify which babies can safely be monitored and which may benefit from treatment before birth.

 

Not necessarily.

Babies with low-risk CPAM or BPS can almost always be delivered at the referring hospital. A fetal care consultation doesn’t automatically mean changing where a family receives prenatal care or delivers their baby. 

For higher-risk cases, we typically reassess the baby later in pregnancy. A persistently large mass, large cysts that could trap air after birth or concerns about lung development may mean the baby should be delivered at a center prepared to provide specialized neonatal and surgical care. 
 

What happens next depends partly on whether the baby has symptoms.

If a baby has breathing difficulties or needs oxygen, we may treat the lung mass during that hospitalization. If the baby is completely asymptomatic, I typically recommend detailed imaging at about 2 to 3 months of age to help guide next steps. 

There is some debate about whether asymptomatic CPAMs should be removed. My approach is to recommend removal because of potential future risks, including infection and, in some cases, malignancy. 

The diagnosis is only the beginning

Finding a fetal lung mass can sound alarming, but the initial ultrasound doesn’t determine what happens next.

We look at what the mass is, how it changes over time and how it is affecting the baby. Those answers help us determine the right plan for the pregnancy, delivery and care after birth.

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