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Lung | Pleural Effusions

Essential Information

  • A pleural effusion is an accumulation of fluid around the lungs.
  • A pleural effusion may develop in isolation, as a “chylothorax” or as a part of generalized hydrops associated with large congenital pulmonary airways malformations, or in association with other fetal conditions.
  • Severe pleural effusions lead to increased pressure in the chest, impacting on lung development and heart function.
  • Treatment of severe pleural effusions may include thoraco-amniotic shunting, where a catheter is inserted into the fetal chest cavity to allow the excess fluid to drain away from the lungs, allowing them to expand.


A pleural effusion is an accumulation of fluid around the lungs. Pleural effusions can be isolated (primary hydrothorax, also called called chylothorax) or secondary to other conditions such as bronchopulmonary sequestrations (BPS), CDH, cardiac anomalies, fetal infections, metabolic disorders, chromosomal or syndromal disorders. Pleural effusions are seen on ultrasound as a black rim of fluid in the fetal chest. Sometimes, pleural effusions can be a sign of fetal heart failure. They are then associated with fluid in the fetal abdomen (ascites), fluid around the heart (pericardial effusion) and fluid under the skin. When fluid effusions are present in multiple compartments in the setting of heart failure, this is called ‘hydrops’. 

Mild to moderate primary hydrothorax, which does not lead to heart failure, displacement of the heart or severe lung compression has good outcomes when managed conservatively and the outlook for a normal life is excellent.

Severe pleural effusions, however, lead to increased pressure in the chest, thereby impacting lung development and heart function. Severe effusions can sometimes lead to heart failure and hydrops. Without prenatal treatment, these fetuses will only survive in 25% of cases.

Every fetus with suspected pleural effusions, needs to be referred to a specialized perinatal center such as the Fetal Medicine Unit at Mount Sinai Hospital. A detailed ultrasound will be performed to determine the extent and the cause of the pleural effusion. Sometimes, a detailed heart ultrasound (echocardiogram) will be required. Further investigations include maternal blood work to determine the cause of the effusion, fetal karyotype or microarray testing and tests to exclude fetal infections.

Ongoing ultrasounds are used to monitor the severity of the effusion and to look for signs of heart failure.

Fetuses with mild hydrothorax do not require any prenatal therapy. After birth, the infant will be assessed by a neonatologist. Sometimes the effusion(s) may need to be drained after birth by use of a special catheter (chest tube) and babies may be fed with a special formula to prevent re-accumulation of the fluid.

Fetuses with moderate and severe hydrothorax may benefit from antenatal drainage of the effusion.