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.

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Congenital pulmonary airway malformation