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Lung | Congenital pulmonary airways malformation (CPAM)

Congenital pulmonary airways malformations (CPAM) are a group of conditions affecting the fetal lungs (Congenital cystic adenomatoid malformations (CCAM) and bronchopulmonary sequestrations (BPS)). With CPAMs, the normal fetal lung tissue is partially replaced with abnormal, cyst-like tissue which does not function properly. Most fetuses diagnosed with a CPAM have an excellent outcome. Rarely, the lesion can grow rapidly and cause the fetus to accumulate a pleural effusion around the lungs or to develop hydrops.

Essential Information

  • Congenital pulmonary airways malformation (CPAM) refers to abnormal fetal lung tissue that replaces part of the normal fetal lung. CPAMs include congenital cystic adenomatoid malformations (CCAM) and bronchopulmonary sequestrations (BPS).
  • Most cases of CPAM have excellent outcomes. Rarely, CPAMs may have large cysts (macrocystic) and grow rapidly. These can lead to fetal heart failure.
  • Heart failure in the fetus may present as a condition called “hydrops”, which is an accumulation of fluid under the fetal skin or in the fetal abdomen or chest. Fetuses with this condition are very sick and may not survive.

Overview

CPAMs may be composed of small cysts (microcystic) or large cysts (macrocystic) and the lesions themselves may vary in size significantly. Most cases of CPAMs are associated with excellent outcomes after birth. Rarely, these lesions may grow to become very large and become life-threatening to the fetus. In these cases, the fetal lungs may be underdeveloped, and heart failure may develop. Pleural effusions may be seen as part of hydrops, as described above.

Bronchopulmonary sequestrations (BPS) are lung lesions that have a blood supply, but no air supply.  Very large BPS lesions may lead to hydrops.

Detailed ultrasound and fetal echocardiography (targeted ultrasound of the fetal heart) are critical in assessing the impact of these lesions on heart and lung function.

Mothers must also be monitored closely because, rarely, hydrops may cause the mother to develop a severe condition called “mirror syndrome”. In this case, mothers may develop high blood pressure, and fluid may accumulate, similarly to the fetus, in their lungs.

Treatment

Fetuses with moderate to severe pleural effusions or large macrocystic CPAM/CCAM lesions may benefit from a fetal procedure called “thoraco-amniotic shunting”. A small catheter, or shunt, is placed into the fetal chest under ultrasound-guidance which allows continuous drainage of the excess fluid away from the lungs. This relieves the built-up pressure in the chest cavity and allows normalization of heart function and fetal lung development. In 50% of cases, this allows the hydrops to resolve. If there is an excessive build-up of amniotic fluid (polyhydramnios), some fluid may be removed at the same time. Occasionally, the shunt may become blocked or move away from its ideal position and may need to be replaced. This occurs in approximately 10-15% of cases.  The shunt(s) remain in place until delivery, and unless there are other reasons for a caesarean section, delivery can be normal. The average gestational age at delivery after chest shunt insertion is 34 to 35 weeks. In our experience, survival after birth after in-utero chest shunt insertion is 65-70% overall (55% in fetuses with hydrops, but 85% if there is no hydrops). Our team at Mount Sinai is world-renowned for performing this procedure.

Bronchopulmonary sequestrations (BPS) are lung lesions that have a blood supply, but no air supply.  Very large BPS lesions may lead to hydrops and the prognosis is very poor. In such cases, lesions may be amenable to blockage of the blood supply to the BPS using either interstitial laser, radiofrequency ablation (RFA) or thrombogenic coils. Great care must be taken to avoid collateral damage to adjacent healthy tissues.

Referral Information (for physicians)

Inclusion criteria

Severe unilateral or bilateral pleural effusions or large macrocystic lung lesions causing significant mediastinal shift and hydrops.

Exclusion criteria

Associated severe genetic or anatomic anomalies. Hydrops is NOT an exclusion criterion.

Practically

Urgent referral is required in the presence of hydrops. Fetal echocardiography can be done locally or arranged here at SickKids. Genetic testing will be offered at the time of the procedure. These procedures may require a 24-hour hospitalization. In the presence of hydrops, surveillance for “mirror” syndrome is warranted. Post-operatively, out-of-province patients will be referred back to their local centre for ongoing antenatal care and delivery. Local patients will be followed further at Mount Sinai and SickKids hospitals.