Congenital cystic adenomatoid malformation

Congenital cystic adenomatoid malformation or CCAM is a disorder where, in the developing fetus, tissue of the lobe of a lung does not develop properly and instead becomes a cyst. In many cases, the disorder is completely asymptomatic. However, when it is discovered, surgery to remove the cyst is indicated as the cyst will continue to grow and will never develop into useful lung tissue.
CCAM can be found on a fetal ultrasound where it appears as a bright white mass where the developing lung should be. If a fetus has the condition, it's progress is monitored. In most cases, surgery is done after birth. However, in some cases, pre-natal intervention is necessary:
*The cyst may develop edema of the chest which will interfere with the developing lungs and heart. In such cases, a shunt can be inserted to drain fluid into the amniotic sac.
*The cyst itself may grow so large that it will press against the lungs and heart. If the fetus is viable, a special type of surgery known as an EXIT procedure can be performed - a combination of a Cesarean section to expose the fetus, followed by surgery while the umbilical cord remains attached until the cyst is removed.
*If the fetus is not viable, it is possible, but dangerous, to do fetal surgery to remove the cyst. However, in such cases, the fetus will almost always die before delivery, but it's chances improve to 60% with surgery.
*Small cysts can be treated with a course of steroids to avoid surgery, and this method has a success rate of at least 75%.
Congenital cystic adenomatoid malformation at Wikipedia