Chylothorax – Pleural effusion

Chylothorax – Pleural effusion


This represents an accumulation of fluid in the pleural cavity, and is classified either as being isolated or in association with fetal hydrops. The isolated form is commonly chylous in nature, unilateral, and right-sided. It results from either a malformed or torn thoracic duct. A minority of isolated effusions are found in association with a range of other conditions.


Chylothorax (pleural effusion) is characterised by echo-free spaces lying between the lungs, chest wall and diaphragm.

Excessive pleural fluid has been reported as early as 8.5 weeks gestation by endovaginal sonography. Its presence should result in a thorough search for associated abnormalities and fetal hydrops in order to determine whether the effusion is isolated or not.

Bilateral pleural effusions are seen in 80% of cases. When pronounced this results in lung compression and the secondary sonographic findings of butterfly-shaped lungs. The compressed lungs are sonographically dense and are associated with pulmonary hypoplasia.

Mediastinal compression may result in displacement of the fetal heart and obstruction of venous return giving rise to hydrops and polyhydramnios.

Doppler evaluation of flow in the inferior vena cava may demonstrate an increased amount of reverse flow in the wave if the pleural effusion is secondary to cardiac failure.

Serial follow-up of pleural effusions has demonstrated spontaneous resolution on several occasions. Pleural effusions may be part of a generalised hydropic fetal condition of immune or non-immune origin.

Underlying structural anomalies (pulmonary lymphangiectasia, cystic adenomatoid malformation of the lung, pulmonary sequestration, diaphragmatic hernia, chest wall hamartoma) are all associated with pleural effusions, as are fetal tumours obstructing venous return to the heart. Cardiac structural and functional anomalies, with or without arrhythmias, may predispose to pleural effusions. Viral infections have also been implicated.

Differential Diagnosis

Large pericardial effusions may often mimic pleural effusions.

Sonographic Features

  • Anechoic intrathoracic fluid collection.
  • May be associated with hydrops as evidenced by pericardial effusion, ascites and polyhydramnios.

Associated Syndromes

Associated karyotypic abnormalities include:

  • Trisomy 21
  • Monosomy X
  • Trisomy 13