Isolated Pleural Effusions

• What is Pleural Effusion?

Pleural effusion refers to a collection of fluid around the fetal lungs. Although there may be a recognisable underlying cause of this fluid accumulation, in many cases the cause remains unknown. The significance of pleural effusions depends on how much fluid is present and whether there is associated fluid collection in other parts of the fetus (medical terms: ascites, edema, hydrops).

• What effect will pleural effusions have on the fetus?

The finding of pleural effusions alone does not mean that the lungs have been or will be damaged. Whether there will be any effect on the fetus depends on whether there appears to be any associated abnormality present (see further tests below) and on whether the fluid accumulation resolves. Pleural effusions can be large or small, the person performing your scan will explain the exact findings to you during your scan.

If the pleural effusions are small and there are no other obvious abnormalities present, in most cases the fluid will just disappear within the next few weeks and the lungs will develop normally. Occasionally the fluid does not disappear or the amount increases.

If the pleural effusions are large, they will probably not disappear and so you many be advised that the fluid needs to be drained from around the fetal lungs. This will involve the introduction of a small plastic tube (shunt) which links the fluid filled cavity to the amniotic fluid so that the fluid can automatically drain away. Although this procedure does carry a risk of miscarriage, (about 5%), in most cases where this is performed the lungs will go on to develop normally. Draining the fluid may also mean that it is easier to look for other indications as to the cause of the pleural effusions.

If the fluid is not drained in these cases, there is a risk that the lungs will become compressed so that the fetus cannot 'practice' breathing and in this case the lungs cannot function at birth. The medical term for this lethal condition is Pulmonary hypoplasia. Alternatively the fluid collection can sometimes cause compression of other organs and vessels which can cause collection of fluid in and around the fetus. The medical terms for these conditions are hydrops and polyhydramnios. These conditions can increase the likelihood of early labour.

• What other tests will I be offered?

You will be offered another scan appointment in about two weeks to check whether the pleural effusions are resolving. Depending on the size of the effusions and on whether a shunt has been introduced you may also be offered further scans throughout  the pregnancy.

In about 10% of cases pleural effusions are associated with chromosomal abnormalities like Down syndrome. Therefore you will be offered the option of a diagnostic test - cordocentesis or amniocentesis - to exclude this possibility. If a shunt is being introduced anyway, the sample will be taken at the same time.

One of the other causes of pleural effusions is viral infection in the fetus. A simple maternal blood test will be carried out to exclude some of the more common kinds of infection.