Congenital pulmonary airway malformation

A congenital pulmonary airway malformation, abbreviated CPAM, is a lung malformation that usually affects a single lobe of one of the lungs, and forms during fetal development.

The old name for CPAMs was congenital cystic adenomatoid malformation, because they have both “cysts” and “glands” in them, but are terribly malformed and disorganized.

CPAM cysts are continuous with the airways, so they’re filled with fluid in utero, and become filled with air after birth.

The cause of CPAMs isn’t known. It isn’t even known whether they’re a developmental failure or if they’re a type of hamartoma, which is a benign overgrowth of tissue.

Sometimes, the growing CPAM can prevent normal healthy lung tissue from developing - causing pulmonary hypoplasia - which is underdevelopment of the lungs.

Also, a CPAM can push on the heart or large veins, causing blood to back up throughout the fetus’s veins. When that happens, fluid can start to leak into the fetal tissues, a condition called fetal hydrops.

Whether or not any of this happens largely depends on the size and location of the CPAM. CPAMs can arise from different spots along the tracheobronchial tree, and that’s how they’re sub-typed.

The five subtypes are named 0 through 4, with type 0 arising from the most proximal airways – the trachea and proximal bronchioles, and type 4 developing all the way down in the alveolus.

Type 0 CPAMs develop at the trachea or proximal bronchus with small cysts, but are pretty rare. Type 1 CPAMs, which develop in the distal bronchi and proximal bronchioles, are the most common, and have one or more large cysts, with tissue like cartilage in between the cysts.

Type 2’s come from the terminal bronchioles and have smaller cysts. Type 3s arise almost all the way down to the alveolus, and have cysts that are so small that they look like a solid mass.

And type 4s develop in the alveoli and have large cysts. In addition to the size of the cyst, the five types also differ in the kind of epithelial cells that line the inside of the cysts.

Type 1’s are lined with ciliated, pseudostratified, columnar epithelium – the same epithelium that makes up normal bronchi.

Whereas type 4’s are lined with flat alveolar cells, which is just like the alveoli from that they come from. Symptoms of babies born with CPAMs vary.

Some are asymptomatic, whereas others with pulmonary hypoplasia can have serious breathing difficulties. CPAMs can also get repeatedly infected, and can also lead to a pneumothorax if the CPAM develops a hole someplace that allows air to go from the airway right into the pleural cavity.

Finally, CPAMs are associated with lung cancer, specifically bronchoalveolar carcinoma and pleuropulmonary blastoma. Most CPAMs are diagnosed on prenatal ultrasound, and if one is seen, then there’s typically a follow up fetal echocardiogram – which is a dedicated ultrasound of the heart – as well as a fetal MRI to look for any associated malformations.

For example, type 2 CPAMs are often accompanied by kidney and heart defects. CPAMs can grow, stay the same size, or even regress during the pregnancy, so they need to be followed over time.

If fetal hydrops develops, it may be necessary to pull fluid out of the CPAM to make is smaller, or to place a shunt from the cyst to the amniotic cavity to help it drain, or to do surgery to remove the entire CPAM.

Alright - as a quick recap - Congenital pulmonary airway malformations are cystic lesions that occupy some or all of a lobe of a lung.

They can cause a number of problems like pulmonary hypoplasia, pneumothorax, and recurrent infections, so they are usually surgically removed.