In rare cases, the cystic mass grows so large as to limit the growth of the surrounding lung and cause pressure against the heart.

CPAM type 2 (with medium-sized cysts) often has a poor prognosis, owing to its frequent association with other significant anomalies.

However, 25% develop cyanosis, pneumothorax, and show signs of increased breathing difficulty (tachypnoea and intercostal retractions).

Identifying characteristics on the sonogram include: an echogenic (bright) mass appearing in the chest of the fetus, displacement of the heart from its normal position, a flat or everted (pushed downward) diaphragm, or the absence of visible lung tissue.

The disappearance is due to the malformation becoming filled with fluid over the course of the gestation, allowing the ultrasound waves to penetrate it more easily and rendering it invisible on sonographic imaging.

When a CPAM is rapidly growing, either solid or with a dominant cyst, they have a higher incidence of developing venous outflow obstruction, cardiac failure and ultimately hydrops fetalis.

The lung mass volume is determined using the formula (length × width × anteroposterior diameter ÷ 2), divided by head circumference.

Many patients have surgery, typically before their first birthday, because of the risk of recurrent lung infections associated with CPAMs.

Some pediatric surgeons can safely remove these lesions using very tiny incisions using minimally invasive surgical techniques (thoracoscopy).

In rare extreme cases, where fetus's heart is in danger, fetal surgery can be performed to remove the CPAM.

Recently, several studies found that a single course of prenatal steroids (betamethasone) may increase survival in hydropic fetuses with microcystic CPAMs to 75-100%.

[8] A 2023 review found that the overall prognosis for congenital pulmonary airway malformation, when diagnosed prenatally, was excellent.