What is pleural effusion, pericardial effusion and non-immune hydrops?

The abnormal collection of fluid within two or more compartments in the fetus is called “Hydrops.” If the accumulation of fluid is not due to an immunological incompatibility between the mother and the fetus, the condition is called “Non-immune hydrops fetalis” or NIHF. The causes of NIHF are numerous, and include infections, chromosomal, genetic, hemodynamic, neoplastic, anatomical and others.

Fluid accumulation in the fetal chest may occur within the pleural space (the space between the lungs and the chest wall) or within the sac that surrounds the heart (pericardium). The first are called “Pleural effusions” and the second “Pericardial effusion.” Either of these conditions may be isolated or as part of a more generalized phenomenon, such as NIHF. Pleural and pericardial effusions may be present in approximately 10% of fetuses with NIHF.

What are the consequences of pleural or pericardial effusions?

The accumulation of fluid within the chest, whether from pleural effusions or a pericardial effusion, is particularly significant because the fluid collection may compress the lungs and prevent them from developing normally (pulmonary hypoplasia). The risk of pleural or pericardial effusions resulting in pulmonary hypoplasia will depend both on the size of the effusions (or how much the lungs are constricted), the gestational age at which they develop, and the duration of the effusions. The earlier the gestational age, the larger the effusion and the more prolonged the effusions are, the more likely the fetus will develop pulmonary hypoplasia. Pulmonary hypoplasia may result in neonatal death, if the baby cannot be adequately oxygenated.

How are pleural and pericardial effusions diagnosed?

The diagnosis of pleural effusions and pericardial effusion can be made with ultrasound. In pleural effusions, the lungs are compressed towards the midline by the fluid within the pleural space. The effusion may be only on one side or on both sides. In pericardial effusions, both lungs are compressed towards the back of the chest. In either case, the size of the effusion can be monitored by measuring the distance between the chest wall and the lung surface (in pleural effusions) or the cardiac surface (in pericardial effusions) on a cross-section of the chest. The size of the lungs may also be estimated using a gestational-age independent ultrasound marker (The Quantitative Lung Index, or QLI) developed by Dr. Quintero and his associates.

How are patients with pleural or pericardial effusions assessed?

Patients with pleural or pericardial effusions are offered a comprehensive workup that includes maternal serum testing for evidence of an infectious cause and to rule out an immunological incompatibility. A thorough ultrasound examination is performed to rule out the presence of congenital anomalies. Fetal Doppler studies are also performed to rule out a hemodynamic cause or the possibility of fetal anemia. A fetal echocardiogram is indicated to rule out the presence of a congenital heart disease or abnormal cardiac function. An amniocentesis (obtaining amniotic fluid from the bag of waters with a thin needle under ultrasound guidance) may also be offered to check for chromosomal and other genetic causes and to rule out a fetal infection more directly. Despite the extensive workup, the actual cause of the effusions may not be determined in a significant number of patients.

Can pleural or pericardial effusions be treated antenatally?

If the workup is negative, fetuses with pleural or pericardial effusions may be offered antenatal treatment in the form of a thoraco-amniotic shunt. This involves the placement of a shunt (plastic catheter) between the fluid collection and the skin outside the chest. Because the pressure inside the fetal chest is greater than the pressure in the amniotic cavity, the fluid drains out of the fetus. The procedure is done under ultrasound guidance. Tan-colored fluid is usually present, which in the case of pleural effusions may represent abnormal drainage of lymph into the pleural space (chylothorax). Placement of the shunt should result in a decrease in the size of the effusion with simultaneous expansion of the fetal lung. Lack of lung expansion after shunt placement may be associated with a poor prognosis. The thoracoamniotic shunt may become dislodged, either inside the fetus, or outside into the amniotic cavity. In such cases, depending on the parameters mentioned above, a repeat procedure may be indicated if expectant management or delivery are not better options.