Lung | Congenital pulmonary airways malformation (CPAM) and/or severe pleural effusions

Congenital pulmonary airways malformation (CPAM) is a group of conditions that affects the fetal lungs. With CPAM, 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 excellent outcomes. Rarely, the lesion can grow rapidly and cause the fetus to accumulate fluid around its lungs, called a pleural effusion. Pleural effusions may also develop as a result of numerous other fetal conditions not related to the lungs. Irrespective of the underlying cause, severe pleural effusions may need to be drained before birth.

Essential Information

  • Congenital pulmonary airways malformation (CPAM) refers to abnormal fetal lung tissue that replaces part of the normal fetal lung.
  • Most cases of CPAM have excellent outcomes. Rarely, CPAMs may be composed of 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.
  • A pleural effusion is a specific term describing the accumulation of fluid around the lungs. This may develop as a part of hydrops associated with large CPAMs, or in association with numerous other fetal conditions. Severe pleural effusions may lead to increased pressure in the chest, thereby impacting lung development and heart function.
  • Treatment of severe pleural effusions may include a fetal surgery called “thoraco-amniotic shunting”, where a catheter is inserted into the fetal chest cavity to allow the excess fluid to drain away from the lungs.


A pleural effusion refers to an accumulation of fluid around the lungs. In the fetus, pleural effusions are often seen as part of a condition called “hydrops”, whereby fetal heart failure results in the abnormal accumulation of fluid in various body compartments such as the lungs, the heart, the abdomen and the skin.

Multiple conditions have been described in association with pleural effusions in the fetus, including structural heart disease, fetal infections, metabolic disorders, genetic syndromes, or congenital chylothorax. Pleural effusions have also been described in association with congenital pulmonary airways malformations (CPAMs), which refer to a group of conditions whereby portions of the fetal lung tissue are replaced with abnormal cyst-like tissue that does not function normally.

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.

Ultrasound and fetal echocardiography (targeted ultrasounds of the fetal heart) are critical in assessing the severity of the impact of the pleural effusion on the overall 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 or in their lower limbs.



Fetuses with moderate to severe pleural effusions may benefit from a fetal procedure called “thoraco-amniotic shunting”. Here, the fetal chest cavity is accessed via the maternal abdominal wall, under ultrasound-guidance. A small catheter, or shunt, is placed which allows for continuous drainage of the excess fluid away from the lungs. This relieves the built-up pressure in the chest cavity and allows for normalization of the heart function and fetal lung development. Occasionally, the shunt may become blocked or move away from its ideal position and need to be repositioned or replaced. This occurs in approximately 10-20 per-cent of cases. The average gestational age at delivery after chest shunt insertion is 34 to 35 weeks’ gestational age. Survival after birth after in-utero chest shunt insertion is approximately 55 per cent in fetuses with hydrops, but is improved to 85 per cent if the chest shunt is placed before hydrops develops.

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.


Urgent referral is required in the presence of hydrops. An echocardiography can be done locally or at The Hospital for Sick Children (SickKids). Genetic testing will be offered at the time of the procedure. These procedures typically require a 24-hour hospitalization. In the presence of hydrops, surveillance for mirror syndrome is warranted. Postoperatively, out-of-province patients will be referred back to their local centre for further antenatal care and delivery. Local patients will be followed further at Mount Sinai Hospital and SickKids.