Prevalence:

• Isolated congenital chylothorax is found in about 1 in 10,000 births.

Ultrasound diagnosis:

• Usually presents with polyhydramnios at around 26 weeks’ gestation.
• Unilateral (25% of cases) or bilateral anechoic area surrounding the lung. Subjectively classified as mild, moderate or severe and in the latter case if unilateral there is mediastinal shift.
• In half of the cases the effusion is isolated and in the other half there is associated hydrops with skin edema and / or ascites.

Associated abnormalities:

• Chromosomal defects, mainly trisomy 21 and monosomy X, are found in 10% of cases.
• Noonan syndrome (autosomal dominant but >90% are due to de novo mutations; cystic hygromas, hypertelorism, pulmonary stenosis, fetal growth restriction), is found in <5% of cases of isolated hydrothorax.
• In the case of associated hydrops there is a wide range of genetic conditions, especially if there are other defects.

Investigations:

• Detailed ultrasound examination, including echocardiography.
• Invasive testing for karyotyping and array.
• Specialist investigations, including infection screen and assessment for anemia and metabolic disorders, may be necessary in the case of hydrops.

Fetal therapy:

• In severe unilateral or bilateral pleural effusions placement of thoraco-amniotic shunts restores the normal intrathoracic anatomy and results in resolution of associated hydrops and polyhydramnios. An alternative to shunting is pleurodesis in which a sclerosant substance is injected in the pleural cavity.

Follow up:

• Ultrasound scans every 2 weeks to monitor the evolution of the pleural effusions and associated hydrops. Insertion of new shunts may become necessary if these are blocked or displaced.

Delivery:

• Place: hospital with neonatal intensive care.
• Time: 38 weeks.
• Method: cesarean section, if there is severe hydrops. In fetuses with shunts, these need to be clamped at delivery to prevent the development of pneumothorax.

Prognosis:

• Isolated effusion: survival is >90%.
• Effusions with hydrops: in 50% of cases the hydrops resolves after thoraco-amniotic shunting and in these cases the prognosis is good. If there is no resolution of hydrops, there may be an underlying genetic syndrome or infection and in these cases the prognosis is poor.

Recurrence:

• Isolated or associated with infection: no increased risk.
• Part of trisomy: 1%.
• Part of genetic syndrome: up to 25%.