Congenital pulmonary airway malformation (CPAM) is a rare lung condition that forms before birth, occurring in roughly 1 in 25,000 to 35,000 babies. It happens when a section of lung tissue develops abnormally during pregnancy, creating fluid-filled sacs called cysts instead of normal, functioning airways. CPAM is the most common congenital lung defect, and most babies do well with proper monitoring and treatment.
How CPAM Forms During Pregnancy
Normal lung development follows a precise sequence during pregnancy. In babies with CPAM, that sequence stalls at a certain stage, and a cluster of cells grows into cyst-like structures instead of healthy lung tissue. The timing of the disruption determines which part of the lung is affected and what the abnormal tissue looks like. Several genes involved in cell growth and tissue development play a role, but CPAM is not typically inherited or caused by anything a parent did during pregnancy.
The malformation usually affects only one lobe of the lung and stays confined to that area. In most cases, the rest of the lung develops normally, which is one reason the long-term outlook is generally good.
Types of CPAM
Doctors classify CPAM into five types (0 through 4) based on where in the airway the abnormal tissue originates and how large the cysts are.
- Type 1 is by far the most common, accounting for about 70% of all cases. It produces larger cysts, typically within a single lobe of the lung.
- Type 2 is the second most common. It features many smaller cysts that generally don’t push on surrounding structures.
- Type 3 is less common and tends to involve an entire lobe. These lesions appear more solid than cystic and can compress the other lobes.
- Type 4 is very rare and consists of thin-walled cysts at the outermost edges of the lung.
- Type 0 originates in the main airways and is the rarest and most severe form.
For parents, the type matters mainly because it influences how large the malformation appears on imaging and how it might behave over time. Your baby’s care team will use this classification to guide monitoring and treatment decisions.
How CPAM Is Found
Most CPAMs are detected during a routine prenatal ultrasound, typically in the second trimester. The malformation shows up as a mass in the chest that looks different from surrounding lung tissue. Once spotted, doctors calculate something called the CPAM volume ratio (CVR), which compares the size of the lesion to the baby’s head circumference. A CVR above 1.6 is a warning sign that the baby may develop fluid buildup, a condition called hydrops, which can be dangerous.
Many CPAMs stay small or even shrink on their own before birth. Serial ultrasounds, usually every one to two weeks during the most active growth period, track whether the lesion is growing, stable, or getting smaller. If the CVR stays below 1.6 and there are no signs of hydrops, the pregnancy is typically monitored closely but otherwise proceeds normally.
Prenatal Treatment for High-Risk Cases
When a CPAM grows large enough to threaten the baby’s health before birth, doctors can administer steroid injections to the mother. This treatment is usually given around 22 to 25 weeks of pregnancy. In studies, steroid treatment slowed or reversed lesion growth in the majority of cases, with one study reporting that growth slowed in about 62% of treated pregnancies. The steroids also improved the shifting of the heart and other chest structures caused by a large mass pressing on them.
In very rare, severe cases where hydrops has already developed and steroids aren’t enough, fetal intervention to drain the cysts may be considered. These situations are uncommon, and most families will not face them.
What Happens After Birth
Some babies with CPAM are born with breathing difficulty: rapid breathing, flared nostrils, grunting, or a bluish tint to the skin. These babies typically need imaging and may require surgery in the first days or weeks of life. However, many babies with CPAM are born without any obvious symptoms at all, especially when the lesion is small. These infants breathe normally, feed well, and appear healthy.
Even when a baby seems fine at birth, doctors will order a CT scan of the chest (usually within the first few months) to get a detailed picture of the malformation’s size, location, and type. This scan guides the decision about whether and when surgery is needed.
Surgery and Timing
Surgery to remove the affected portion of lung is the standard treatment for CPAM. For babies with symptoms, the operation happens early. For babies without symptoms, the general consensus is that the malformation should be removed before the child’s first birthday. Research has shown that elective surgery is equally safe anywhere between 1 and 12 months of age, so your surgical team will choose timing based on your baby’s individual situation.
The most common operation is a lobectomy, where the surgeon removes the lobe of the lung containing the malformation. This can be done two ways: through a traditional open incision in the chest (thoracotomy) or through small incisions using a camera and specialized instruments (thoracoscopy). Both approaches have similar complication rates and very low mortality. The minimally invasive approach is associated with a slightly shorter hospital stay, with a median of about 3 days, and a meaningfully lower risk of long-term musculoskeletal problems. One study found scoliosis developed in 54% of children after open surgery compared to just 9% after the minimally invasive approach. About 15% of thoracoscopic procedures end up converting to an open approach during surgery, which is a normal part of the surgical plan rather than a complication.
Why Doctors Recommend Removing Asymptomatic CPAMs
Parents often wonder why surgery is recommended for a baby who seems perfectly healthy. There are two main reasons. First, CPAMs can become infected over time, causing recurrent pneumonia in the same part of the lung. Second, there is a meaningful risk that abnormal lung tissue can harbor or develop tumors. A systematic review in adults found that about 23 to 26% of CPAMs contained a tumor at the time of surgical removal, and roughly a quarter of those were in patients who had no symptoms at all. Removing the lesion early eliminates both of these risks.
Recovery and Long-Term Outlook
Young lungs have a remarkable ability to compensate after surgery. When a lobe is removed in infancy, the remaining lung tissue expands to fill the space. Studies tracking children after lobectomy have found that total lung volume reaches roughly 90% of the predicted normal value over time. In the first month after surgery, babies commonly show signs of mild airway changes on breathing tests. By one year post-surgery, lung function testing shows no significant difference between children who had CPAM surgery and healthy children of the same age and size.
Researchers note that the compensating lung may not be entirely identical to tissue that developed normally, with some studies detecting subtle differences in airflow distribution and air trapping. In practical terms, though, most children who undergo CPAM surgery in infancy go on to live active, unrestricted lives without chronic breathing problems. Long-term follow-up with a pediatric pulmonologist helps ensure that lung growth stays on track as your child gets older.