Fetal pleural effusions (FPE) refer to an accumulation of pleural fluid in utero. It can refer to either a fetal chylothorax or a fetal hydrothorax.

Pathology

A fetal pleural effusion can occur as part of hydrops fetalis, in association with other anomalies without hydrops or in isolation - primary pleural effusion/primary fetal hydrothorax (PFHT).   

Causes

Any cause of hydrops fetalis is a potential aetiological factor in a fetal pleural effusion.

Associations

In addition to hydrops fetalis, pleural effusion can be associated with numerous other underlying anomalies:

• congenital cardiac anomalies: ~ 5% of non hydropic pleural effusions ¹

• underlying congenital lung anomalies

  • pulmonary lymphangiectasia

  • congenital pulmonary airway malformation

  • bronchopulmonary sequestration

  • congenital diaphragmatic herniation

  • chest wall hamartoma

  • pulmonary venous atresia

• chromosomal anomalies ^1,3  (can be present in ~ 50% with an additional sonographic abnormality and ~ 12% without an additional sonographic abnormality ⁹) 

  • Down syndrome: ~ 20% (range 5-33%) of non hydropic pleural effusions ^1,7

  • Turner syndrome: especially with a 1^st trimester pleural effusion

  • trisomy 18:

• polydactyly: ~ 1% of non hydropic pleural effusions ¹

Radiographic features

Ultrasound

Classically seen as anechoic fluid surrounding one or both the lungs (which are echogenic) - batwing appearance. 

Ancillary sonographic features include:

• may show other features of hydrops if it occurs in association

• there maybe presence of polyhydramnios (if severe)

Treatment and prognosis

The clinical course is variable and dependent on aetiology. The presence of a pleural effusion early in pregnancy (i.e. first trimester) is often associated with a poor fetal outcome ⁵.

Management options are also dependent on other underlying factors:

• thoracocentesis and drainage of the effusion: fluid can however reaccumulate within 24-48 hours

• insertion of pleural-amniotic shunts