What do we actually know about lung malformations? Q&A with Dr Shaun Kunisaki
Over the last 20 years, research and clinical experience around congenital lung malformations (CLMs) has advanced significantly. These abnormalities are diagnosed more often (and earlier) than before, we have better tools to assess risk in pregnancy and at birth (including the CVR), and clearer frameworks for postnatal evaluation and treatment. And yet CLMs remain widely misunderstood. To help cut through the noise, we spoke with Dr Shaun Kunisaki—Professor of Surgery at the Johns Hopkins School of Medicine and a Medical Advisor to CPAM Parents—about what we actually know, what’s still debated, and what researchers and clinicians are working hard to understand next.
Dr Shaun M. Kunisaki, MD, MSc, is Professor of Surgery at the Johns Hopkins School of Medicine and Associate Chief of Strategy and Integration in the Division of General Pediatric Surgery at Johns Hopkins Children’s Center, where he directs the Fetal Program in General Pediatric Surgery. In addition, he serves as Director of Pediatric Esophageal Surgery at Johns Hopkins Children’s Center.
What does current research say about how rare CLMs are? Are some types rarer than others?
Dr Kunisaki: Congenital lung malformations (CLMs) are rare, but most large children’s hospitals still see them regularly, at least a dozen cases a year. Overall, CLMs are about as common as cystic fibrosis, a lung disease many people have heard of.
People hear “CPAM, BPS, bronchogenic cyst, CLE” and panic. In plain language, what are the practical differences between these diagnoses?
The differences relate to the type of lung tissue involved, the blood supply to the lesion, and the likelihood of causing problems, either in the womb, at birth, or later in life. That said, these lesions are not cancer, and in many cases the size of the lesion matters more than the exact type of CLM.
Why are experts moving away from CPAM “types” and focusing more on how the lesion grows?
Because lesion size is generally more helpful than CPAM “type” when predicting symptoms at birth and later in life. Research is ongoing as to whether certain lesion subtypes may carry a higher cancer risk if not removed, but this remains an area of active study.
How has CLM management and understanding changed since you first started seeing cases as a pediatric surgeon?
Both diagnosis and treatment have improved significantly since I was a medical student. Hydrops and severe fetal outcomes are less common than earlier reports suggested. Many lesions we see today are smaller because the fetal ultrasound images are sensitive enough to detect them earlier. We now have steroids for treatment of larger high-risk lesions and CVR measurements to help counsel families. When surgery is needed, elective resections are often done minimally invasively through three tiny incisions, with minimal pain and a short hospital stay (often around just two days).
What area of CLM management is still not well understood?
For one, we still don’t know the cause of why CLMs occur. Maternal steroids are effective in terms of shrinking some large (typically solid/microcystic) lesions, but we really don’t fully understand why they work. There are some small CLMs that probably do not need to be surgically removed, but we don’t yet have a reliable way to identify which which ones can be safely left alone with no complications (infection or, very rarely, cancer, later in life).
When a lung lesion is found—often at the 20-week scan—what are the first three things you want parents to understand right away?
I would say:
A CLM is usually not a sign that something else is seriously wrong with the fetus. Typically the brain, heart, and other organs are normal.
It is not cancer, except in extremely rare circumstances.
Outcomes vary widely, but most babies will not have breathing problems at birth, and overall outcomes are typically very good.
What does current research say about how and why CLMs develop?
There are a lot of theories, but exactly how they develop is unclear. The lung is an incredibly complex organ. Many experts think CLMs result from an error in gene expression during lung development, perhaps in conjunction with blockage in the developing airway.
How often are CLMs linked to genetic conditions or other birth defects?
It’s very rare for CLMs to be associated with genetic problems or major birth defects.
One of the most stressful aspects of navigating a CLM pregnancy is that it is hard to predict which babies will be symptomatic at birth and which won’t. This makes it hard for parents to emotionally and practically prepare. What is our current understanding of which babies will be symptomatic or not?
Yes, I hear you. Hydrops and fetal demise are obviously devastating complications but they are rare (under 5% of cases), and fetal surgery is uncommon. For the vast majority of families, the most relevant question is whether the baby will be symptomatic: have breathing problems at birth.
We’ve made a lot of progress in the past decade in predicting which babies are likely to need intensive care and/or early surgery. Some babies with small lesions don’t even necessarily need delivery at a tertiary/major birthing center. Obtaining high-quality ultrasounds is central to this process. In broad strokes, CVR measurements that are consistently under 1.0 cm² are associated with no symptoms at birth in most cases. We worry more when the CVR is consistently more than 1 cm2. These findings were first reported at a national meeting by our team in 2012.
You’ve been involved in research that has proposed the maximum CVR during pregnancy may be more useful in predicting which babies will be symptomatic or not, rather than the last CVR before birth. Why might the last CVR be misleading?
This is a controversial area where I have had rigorous debate with my maternal-fetal medicine colleagues. They are the real experts in ultrasound diagnosis and have long argued that more solid appearing CLMs can become more challenging to measure towards the end of pregnancy because they become the same color as the normal lung tissue. It is like trying to spot a chameleon resting on a tree branch. I wish one value would tell the whole story, but the truth is that multiple CVR values over time are needed to best estimate whether a baby is likely to be symptomatic at birth.
Many families are told lesions “grow until 28 weeks then plateau.” How reliable is that?
There are always exceptions, but most larger CLMs do follow a stereotypical growth pattern: CVR increases until around 26–28 weeks, then the lesion often decreases in size toward term. Many other CLMs don’t grow much at all and instead gradually shrink throughout pregnancy.
Mediastinal shift, polyhydramnios, and “heart compression” can be observed in some CLM babies, particularly before around 30 weeks gestation. Which of these would change management and why?
All of these findings would suggest that the CLM is on the larger side and moving other organs away. Mediastinal shift is quite common and less concerning as an isolated finding. Polyhydramnios and heart compression are more worrisome because some cases can progress to fetal hydrops, a situation where the fetus begins to abnormally retain fluid and the heart begins to fail.
“Vanishing lesions” cause a lot of confusion. If a lesion seems to disappear, is it really gone? What if it doesn’t show on X-ray after birth?
Some lesions do completely disappear but this is rare. More often, the lesion becomes too small to detect on ultrasound or X-ray late in pregnancy (often after ~34 weeks). The more likely scenario is that the CLM becomes too small to detect by ultrasound or x-ray after 34 weeks’ gestation. A CT scan after birth will often confirm that the lesion is still there. This is important because some families are mistakenly told the lesion is gone. In my opinion, all prenatally diagnosed CLMs should have follow-up imaging by CT even if the lesion has been undetectable by other types of imaging studies (e.g. X-ray or ultrasound).
When is fetal MRI genuinely helpful?
This is a very controversial area in CLM diagnosis. Fetal MRI can be helpful in selected cases, but probably not required in most cases if the ultrasound imaging is clear and the lesion is relatively small.
For families going through a sequestration or hybrid lesion diagnosis there is confusion over whether these carry a risk of heart failure. Is there evidence for this?
This is a good question. Sequestrations have an abnormal blood supply, which can place additional stress on the heart. That said, the impact of a sequestration is often best predicted by its overall size and whether it causes heart compression and shifting of other thoracic structures.
What about pulmonary hypertension in newborns with CLMs? Are some types more at risk?
Larger CLMs can interfere with normal lung development. The lungs can be abnormally small (pulmonary hypoplasia), or the blood vessels can have high pressure (pulmonary hypertension). Exactly which large CLMs are most at risk for this is still debated.
Anecdotally, many parents say babies feed better after surgery. Can CLMs cause feeding problems?
I have seen feeding issues in infants with larger CLMs, often when there’s enough mass effect to affect breathing or swallowing, though they’re relatively uncommon with small lesions prior to surgery. There is multicenter data to support this association.
For parents deciding where to deliver: what factors matter when choosing a specialist center vs a local hospital?
There’s still not broad consensus on this, but CVR values can be very helpful in guiding planning. Ultimately, this decision is best made through discussion between the family and their medical team. We can say that the overall risk of needing oxygen at birth for low-risk babies (for example, maximum CVR less than 1.0 and without other concerning features) is very very low, probably around 10%, but for some families that risk still feels too anxiety-provoking to deliver at a local hospital.
Is there any reason to plan an induction or C-section just because of a CLM?
This decision should be best left to discussion between the family and their care team. In most cases, vaginal delivery is feasible, unless there’s another medical reason for a C-section.
What are the most common reasons a newborn would need urgent surgery and how often does ECMO come into play?
There are generally three scenarios that can happen. Urgent surgery is possible, but that is very rare and limited to those with very large lesions with signs of hydrops, history of fetal interventions, and steroids. Some of these children will be ECMO during the lung operation or shortly afterwards if the pulmonary hypoplasia and pulmonary hypertension are severe. Another 10-15% will need surgery within days of birth because the CLM is not allowing the good lung to expand and help with breathing. Again, these babies tend to be the ones with the higher CVRs (consistently well above 1.0), especially towards the end of pregnancy.
Can you walk us through maternal steroids. When are they used, who’s a good candidate, and what response do you hope to see?
Maternal steroids are recommended for larger CPAMs and sequestrations between 22 and 26 weeks’ gestation, especially if they are solid or microcystic. The course is usually two intramuscular injections of betamethasone 24 hours apart.
Steroids are often recommended when the CVR is greater than about 1.6, but they may be given if there are any signs of hydrops regardless of CVR. Some clinicians also consider steroids if there’s a dramatic rise in CVR over a short period (for example 0.5 cm² at 22 weeks increasing to 1.4 cm² at 24 weeks).
Steroids are less effective for macrocystic lesions. Why is that and what are the next steps for these cases if steroids don’t work?
Steroids tend to be less effective for macrocystic lesions, although they’re still used in many cases because they can partially shrink the overall mass. We don’t fully understand why steroids are less effective for macrocystic lesions. If there is still concern that a macrocytic lesion is growing and/or showing signs of associated hydrops, then the next step is usually placement of a thoracoamniotic shunt if there is a large, dominant cyst that can be decompressed. The procedure is done under ultrasound guidance.
Thoracoamniotic shunts sound “minimally invasive,” but they carry risks. What complications should parents understand?
Yes—shunts can be helpful, but they are not risk-free. Any procedure that places a needle through the uterus carries a risk of injury to the uterine membranes with subsequent contractions and possible preterm labor. Shunts can also be difficult to position perfectly, which can reduce how well they drain the cyst. Shunts can also clog or become dislodged with fetal movement, diminishing their effectiveness.
Open fetal surgery and EXIT-to-resection are scary concepts. In 2026, when are these truly on the table?
Open fetal surgery is now rarely performed—perhaps once or twice a year in the US—because other treatments (especially steroids) are often effective in preventing or treating hydrops. Only a handful of centers have reported survivors with good outcomes.
EXIT-to-resection is a well-described procedure in which the baby is partially delivered by C-section and the lesion is removed while the baby remains connected to the umbilical cord and placenta. It can be useful for safely transitioning a baby to life outside the womb after birth, but many centers now favor delivery by C-section followed by rapid transfer to a nearby operating room for resection of the lung mass.