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KEY POINTS
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Key Points

  • May be primary, due to chylous leak, or secondary, in which effusions are part of generalized fluid retention. Secondary hydrothorax is more common in the fetus than the neonate.

  • Sonography demonstrates an anechoic space peripherally around the compressed lungs. If effusion is large there may be mediastinal shift. Polyhydramnios is present in 60% to 70% of cases. Extrathoracic anomalies are frequently present.

  • Prior to 32 weeks of gestation fetal treatment options include: thoracentesis, thoracoamniotic shunting, and thoraco-maternal cutaneous drainage. Thoracentesis should be performed to determine if the effusion is chylous and to obtain a cell count, differential, and culture.

  • Decompression of the fetal chest immediately prior to delivery is controversial.

  • Delivery should occur in a tertiary care center.

  • Up to 5% of cases are associated with a chromosome abnormality, such as Down and Turner syndromes.

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CONDITION
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Fetal hydrothorax (FHT), either unilateral or bilateral, is a pleural effusion that may be primary, due to chylous leak, or secondary, in which the effusions are part of a generalized fluid retention associated with immune or nonimmune hydrops (Holzgreve et al., 1985; Longaker et al., 1989; Laberge et al., 1991). The management of pleural effusion in the fetus is complicated by the difficulty in distinguishing primary from secondary FHT. Secondary FHT is far more common in the fetus than in the neonate (Holzgreve et al., 1985; Hagay et al., 1993). Secondary FHT may be due to a wide variety of maternal and fetal disorders, including chromosomal anomalies, cardiovascular, hematologic, gastrointestinal, pulmonary, metabolic, infectious, and neoplastic, and malformations of the placenta and umbilical cord (Chernick and Reed, 1970; Petres et al., 1982; Gardner et al., 1983; Grena-Ansotegui et al., 1984; Van Gerde et al., 1984; Foote and Vickers, 1986; Nicolaides and Azar, 1990). While the underlying cause of a secondary FHT may be evident from detailed sonographic examination and karyotype analysis, in many instances the cause of the effusion remains obscure even after a postmortem examination (Keeling et al., 1983; Nicolaides et al., 1985).

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INCIDENCE
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Cases of secondary FHT may occur as frequently as 1 in 1500 livebirths (Hutchison et al., 1982; Im et al., 1984; Castillo et al., 1986). The true incidence of primary FHT is uncertain. In a review of cases from five obstetrical hospitals in Montreal between 1980 and 1987, Longaker et al. (1989) estimated that the incidence of primary FHT is 1 case per 12,000 livebirths. The actual incidence of primary FHT may be even higher if one considers that in many cases the condition may remain undiagnosed, it may resolve spontaneously, the fetus may be aborted, or death may occur soon after birth in outlying hospitals before transfer to a tertiary care center (Longaker et al., 1989; Laberge et al., 1991...

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