Pleural effusion or fetal hydrothorax

Pathology description

In the chest, the lungs are surrounded by two layers of membrane called the pleurae, which separate them from the heart and ribs. Fetal pleural effusion or hydrothorax (meaning 'water in the chest') is a build-up of fluid in the space between the lungs and the pleurae. 

The cause of pleural effusion in a fetus may include genetic problems, infections and malformations, especially heart or lung malformations. If no associated malformations are detected and the genetic and infection studies are normal, the most common cause is a problem in the lymph ducts (the vessels that connect the lymph nodes of the body) that after birth is called a primary chylothorax. 

Fetal hydrothorax is rare, occurring in 1 in 5000 pregnancies. 

What are the consequences of fetal hydrothorax?

The prognosis for each individual case depends on the amount of fluid in the chest, which can become so significant that it compresses the lungs, keeping them collapsed, and also the heart, hindering its function. Therefore, hydrothorax can produce: 

• Compression and tightness of the lungs, which if maintained for a long time can hinder their development (pulmonary hypoplasia) and prevent the baby from breathing after birth due to an underdevelopment of the lungs. 
• Compression of the heart, which hinders its normal function and can lead to heart failure, development of hydrops fetalis (accumulation of fluid in other parts of the body) and finally fetal death. 

Diagnosis

Fetal pleural effusion or hydrothorax is easily detected by fetal ultrasound, as the amount of fluid in the chest surrounding the lungs is usually very evident. It usually occurs between the 24th and 30th week of pregnancy. Upon detection, a series of tests should be performed to confirm that it is an isolated finding, and it may also be a chylothorax (lymphatic fluid in the pleurae) with a good postnatal prognosis.

These tests are: 

• High-resolution fetal ultrasound to rule out the presence of other malformations, growth disorders, and alterations in circulation and the amount of amniotic fluid.  
• Fetal echocardiography to perform a specialized evaluation of fetal heart anatomy and function. 
• Magnetic resonance imaging, which can be useful for evaluating chest organs in more complex cases.  
• Amniocentesis for genetic and metabolism studies, which are more frequent when pleural effusion or hydrothorax appears already in the first half of gestation, and to also rule out fetal infections. 

Treatment

The indication for fetal treatment will be established when there is a clear risk of pulmonary complications or the development of hydrops fetalis. There are two treatment options: 

• Thoracentesis (fluid drainage): this is performed with ultrasound monitoring in the consultation room, using a small needle (1 mm) to aspirate the liquid. This relieves pressure on the baby's lungs, which then expand and occupy most of the chest normally, and also improves heart function, reversing any signs of hydrops fetalis. The aspirated fluid will be analysed to determine its origin and this can help identify the cause of its accumulation and guide treatment. In up to 10% of cases a single puncture may be sufficient as a treatment and completely resolves the hydrothorax. But in most cases, especially if there are already signs of hydrops fetalis, the hydrothorax accumulates again 24–48 hours after the procedure. 
• Thoracoamniotic shunt: this is also performed with ultrasound monitoring, but requires local anaesthetic for the pregnant woman and fetal anaesthesia, so it is performed in the operating room. A small plastic tube with spiral-shaped tips is placed, connecting the fetal chest to the amniotic cavity. Due to the high pressure inside the fetal chest, the fluid drains continuously out of the fetus and into the amniotic cavity. This treatment provides relief from hydrothorax, continuous decompression of the fetal chest and offers the best opportunity to prevent hypoplasia of the lungs and the development of hydrops fetalis. 

What appointments are needed for fetal surgery?

An in-patient admission of the pregnant woman will initially last 1 day and afterwards weekly check-ups with examination and ultrasound will be required, and she will have to maintain a low-activity lifestyle mainly at home until the end of pregnancy. Ultrasound scans will allow the monitoring of the correct development of the fetus and the continued correct positioning of the drainage, since its dislocation would lead to the reappearance of hydrops fetalis.

In case dislocation occurs near term, an evacuating thoracentesis just before birth may be necessary to prevent difficulties in the baby's breathing and to aid in its immediate resuscitation. The aim is to ensure that childbirth can be carried out at the end of pregnancy without the need to induce it prematurely. 

In many cases, pregnant women who have babies with fetal pleural effusion or hydrothorax can give birth at their local hospital. But in cases with large effusions in which it has been necessary to perform fetal treatment, babies must be born in a centre like ours, which offers specialized care for both the pregnant woman and the newborn.