**7.1. Definition and incidence**

Fetal hydrothorax (FHT) represents the accumulation of fluid in the pleural cavity, between the parietal and the visceral pleura. It can be unilateral or bilateral. It can be isolated or in the context of a generalized hydrops, or associated with other fetal abnormalities.

The incidence is not specified given the variability of the causes, but in the antenatal period, the secondary causes of hydrothorax are more common [31]. The causes that can lead to the occurrence of fetal hydrothorax are multiple: congenital infection (parvovirus, TORCH), isoimmunization, congestive heart failure, Down syndrome, Turner syndrome. Primary FHT is called chylothorax. Secondary FHT usually appears secondary to chromosomal, cardiac, gastrointestinal and infectious abnormalities. FHT generally precedes the installation of fetal hydrops. The appearance of primary FHT is due to a structural defect in the lymphatic system: the obstruction of bronchomediastinal trunks to the venous system, congenital absence of the thoracic duct, congenital hypoplasia of the pulmonary lymphatic vessel [31, 32]. It is a diagnostic of exclusion. In general, primary FHT occurs as a result of the obstruction of secondary lymphatic drainage to a heterogeneous group of developmental defects of the lymphatic system. Unilateral FHT may happen due to a unilateral pathological process such as: congenital diaphragmatic hernia, cystic adenomatoid malformation, pulmonary hypoplasia.

#### **7.2. Ultrasound diagnosis**

The diagnosis of fetal hydrothorax is established on the axial image of the four chambers of the heart, as an anechoic area around the pulmonary tissue which limits the mediastinum. Effusions can be unilateral or bilateral (**Figure 15**).

or after only a single drainage [32]. Delivery by vaginal route is an option although there is an

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It is mandatory to determine the karyotype in FHT due to the increased risk of association with chromosomal anomalies. Even if the fetus tolerates small isolated effusions, a serial echographic surveillance is required because small hydrothorax can progress rapidly to large effusions that may have negative hemodynamic consequences. Therefore, ultrasound monitoring is recommended every 1 or 2 weeks, due to the risk of polyhidramnios and preterm

If FHT was diagnosed before 24 weeks, the therapeutic interruption of the pregnancy is an option. If the fetus with FHT has more than 32 weeks, then the serial ultrasound at one or 2 weeks distance is recommended, but we can also consider thoraco-amniotic shunt. If the fetus has less than 32 weeks we have three options: thoracocentesis, thoracoamniotic shunt, thoracomaternal cutaneous drainage. The initial step is the thoracocentesis and diagnosis for cell count, culture, or the viral culture. In general, thoracocentesis other than for diagnosis is ineffective because after it is done a re-accumulation of the pleural fluid occurs. The rapidity with which the effusion accumulates after the initial puncture is an indicator of the pleural effusion severity. For this reason, pleural cavity decompression is done through thoracoamniotic shunt. Large FHT is drained through thoracoamniotic shunt especially if hydrops is present. Shunting is especially effective if the fetus has less than 32 weeks of gestation [34]. The failure rate for thoracoamniotic shunt is of 26% [34, 35]. Shunt complications are: blockage, migration, fetal death. If a thoracoamniotic shunt is mounted the incidence of survival increases from 10 to 60%.

Fetal mediastinal cysts are represented by: pericardial cyst, thymic cyst, esophageal duplication cyst, neurenteric cyst. The incidence of these masses is not known because they are rare pathological entities and only case reports are reported. The pericardial cyst is located at the costophrenic right angle level. The pericardial cyst is covered by mesothelium and has fluid content, and is usually asymptomatic. If the size of the cyst is important, then it can be associated with fetal hydrops, or with the change in heart function at birth [17]. If the pericardial

The thymic cyst is very rare, representing 4% of postnatal mediastinal cystic masses [17, 35].

The esophageal duplication cyst exhibits ectopic gastric mucosa, communicating with the gastrointestinal lumen. Sometimes they may not communicate with the gastrointestinal lumen [17, 36]. The communication with the gastrointestinal lumen is located either above the

The neurenteric cyst has a connection with the meninges and the spinal cord and it is usually

Thymic cysts are asymptomatic, but the prenatal diagnosis is possible.

increase incidence of the rate of cesarean section [33].

delivery. Birth in a tertiary center is recommended.

**7.4. Prenatal management**

**8. Fetal mediastinal cysts**

**8.1. Definition and incidence**

cyst size is reduced in size, it can also regress.

associated with congenital scoliosis or spina bifida.

diaphragm or below the diaphragm.

The hydrothorax aspect is that of a peripheral anechoic space in the thorax, compressing the lung tissue. In the case of large bilateral effusions, the aspect is that of the lungs balloting in the rib cage. At the same time, mediastinal shift and the eversion of the diaphragm occur with the displacement of the heart to the contralateral side and they can cause the disruption of the hemodynamic function and the installation of nonimmune hydrops. If the pleural effusion is part of the nonimmune hydrops, then it is also possible to see the edema of the thoracic subcutaneous tissue. It is important to note that FHT associates with the polyhidramnios in over 50% of cases, either due to a mediastinal shift that causes the compression of the esophagus or because of an alteration in the production of amniotic fluid by the compressed lungs.

The differential diagnosis is important because it should be determined whether FHT is primary or secondary. Primary hydrothorax is usually a chylothorax and it is unilateral and is a diagnostic of exclusion. However, the fetus with trisomy 21, Noonan syndrome, and Turner syndrome, may present either unilaterally or bilaterally hydrothorax [31]. For secondary hydrothorax, evidence of specific echographic elements for CDH, CCAM, BPS determines the diagnosis. In the case of the fetuses with hydrops, the presence of fetal anemia should be excluded.

### **7.3. Prognosis**

The most important element of prognosis is whether fetal hydrothorax is associated with non-immune fetal hydrops, because in this situation the fetal mortality is increased. Other negative prognostic factors are FHT associated with cardiac abnormalities or with central nervous system anomalies. The only positive prognostic factor is the presence of FHT without another associated anomaly or other fluid effusion with another location. Isolated small FHT at the fetus without any other abnormalities, without hydrops or abnormal karyotype, has a favorable prognosis, because the fetus usually tolerates well small effusions [31, 32]. What is important to remember is that 10–25% of the cases of chylothorax can regress spontaneously

**Figure 15.** Bilateral hydrothorax: arrow—hydrothorax.

or after only a single drainage [32]. Delivery by vaginal route is an option although there is an increase incidence of the rate of cesarean section [33].
