Fetal Hydrothorax

Fetal hydrothorax is a large collection of fluid in one or both fetal pleural cavities that compresses the lungs and heart. The commonest cause is congenital chylothorax, with secondary causes including hydrops, infection, anaemia, heart failure and chromosomal abnormality. It matters because large bilateral hydrothorax causes polyhydramnios, pulmonary hypoplasia and hydrops, and perinatal mortality is high without treatment.

• Bilateral hydrothorax with hydrops has the worst outlook.
• Risk factors: male fetus, Down syndrome, Turner syndrome, Noonan syndrome, maternal infection.
• Shunting improves survival in selected fetuses.

Women are often asymptomatic. A large uterus from polyhydramnios and reduced fetal movements are late features.

• Large fundal height.
• Breathlessness in the mother from polyhydramnios.
• Differential diagnosis: congenital diaphragmatic hernia, lung mass, pleural effusion with hydrops, pericardial effusion, pulmonary sequestration, cardiac failure.
• Complications: pulmonary hypoplasia, polyhydramnios, hydrops, preterm labour, stillbirth, neonatal respiratory failure and death.

The approach is a detailed scan with tests to find the cause.

• Ultrasound: fluid on one or both sides, compressed lung, mediastinal shift, flattened or inverted diaphragm, polyhydramnios, ascites, skin oedema.
• Fetal echocardiography; middle cerebral artery peak systolic velocity for anaemia.
• Maternal tests: blood group and antibody screen, TORCH serology, parvovirus B19, syphilis, HIV; fluid analysis from thoracocentesis (lymphocytes above 80 percent confirms chylothorax); amniocentesis for karyotype and microarray.
• Lung measurement (lung to head ratio) before and after drainage.

The principle is early drainage by thoracoamniotic shunt when the effusion is large, progressive or accompanied by hydrops, with delivery in a tertiary unit.

• Supportive: refer to a fetal medicine unit; admit for weekly scans; bed rest is not required; counselling about prognosis; deliver in a unit with neonatal intensive care.
• Pharmacological: betamethasone 12 mg IM twice, 24 hours apart, between 24 and 34 weeks and 6 days when delivery is likely; syphilis: benzathine benzylpenicillin 2.4 million units IM once weekly for 3 weeks; cytomegalovirus infection: valaciclovir 2 g oral 6-hourly; anaemia: intrauterine transfusion; indomethacin 25 mg oral 6-hourly for up to 48 hours before 32 weeks for polyhydramnios with symptoms, with repeat scan of the ductus arteriosus; neonatal surfactant (poractant alfa 200 mg/kg endotracheal, then 100 mg/kg) for preterm infants with respiratory distress; octreotide 1 microgram/kg/hour IV infusion, increased daily to a maximum of 10 micrograms/kg/hour for neonatal chylothorax.
• Procedures: thoracocentesis for diagnosis and a test of lung re-expansion; thoracoamniotic shunt for effusions with mediastinal shift, polyhydramnios or hydrops; amnioreduction up to 2 litres for symptomatic polyhydramnios; delivery at 37 weeks or earlier for hydrops that worsens, with immediate neonatal thoracocentesis, chest drain and ventilation.
• Special groups: hydrops with chromosomal disease carries a poor outlook, and genetic counselling guides the decision to intervene.
• Red flags: shunt blockage or displacement, polyhydramnios, hydrops, preterm contractions, reduced fetal movements.
• Follow-up: scan every 1 week after shunting; shunt checks at each scan; newborn chest X-ray and ventilation; paediatric review, with lung function and growth monitoring.