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Fetal Hydrothorax

Unilateral Hydrothorax
Bilateral Hydrothorax

Findings:

A large pleural effusion (hydrothorax) is identified within the right hemithorax. Mass effect represented as downward displacement of the diaphragm is also present. Ascites (arrowhead) was also seen in this case. An additional case of bilateral pleural effuisons is also shown. The moderately echogenic lungs are readily identified.

Discussion:

Fetal pleural effusions may occur either as an isolated sonographic finding or may be part of the complex of findings seen in generalized hydrops fetalis. Isolated pleural effusions, more often seen on the right side, may present as either a small amount of fluid adjacent to the normal lung which maintains its normal contour or a large volume of fluid that exerts mass effect with mediastinal shift and downward displacement of the diaphragm. Bilateral isolated pleural effusions can also occur. While there may be no mediastinal shift with bilateral effusions, the compressive effect on the heart and lungs can be readily seen. Polyhydramnios is often associated with pleural effusion, possibly due to increased intrathoracic pressure that interferes with swallowing. Isolated pleural effusions may progress to generalized hydrops fetalis. The true incidence of fetal pleural effusions is unknown but there have been estimates of an incidence of 1 in 10,000 to 1 in 15,000.

The etiology of isolated fetal hydrothoraces is uncertain. It has been postulated that a congenital chylothorax due to lymph accumulation in the pleural cavity, is the most frequent cause of fetal pleural effusion. Lymph accumulation may result from either overproduction or impaired drainage. Abnormalities of the thoracic duct such as fistulas or atresias may contribute to this abnormality. In the fetus the diagnosis of chylothrorax is made by aspiration of the pleural fluid and identfication of a high lymphocte count, usually greater than 80%. Associated abnormalities are uncommon when an isolated hydrothorax is seen. The two most common associated abnormalities are congenital diaphragmatic hernia and Trisomy 21. Tracheo-esophageal fistula, extralobar pulmonary sequestration and congenital pulmonary lymphangiectasis have also been associated with this condition.

Regardless of the cause, infants born with pleural effusions may present in the neonatal period with severe and often fatal respiratory insufficiency. This may be due to either compression of otherwise normal lung by the fluid or to pulmonary hypoplasia from long-standing compressive effects. As was mentioned earlier, congestive heart failure and generalized hydrops may result from the effects of hydrothoraces. In the case of unilateral large effusions, hydrops may develop from kinking of the inferior vena cava, impairing venous return. In the case of large bilateral effusions, hydrops likely results from increased intrathoracic pressure and a tamponade effect on the heart.

The natural history of fetal pleural effusions is a spectrum varying from resolution in utero, to generalized hydrops fetalis or even death. Mortality for isolated effusions has been reported to be between 15 - 36%. One series reported a mortality rate of 53% , however patients with hydrops fetalis were included in this group. When generalized hydrops fetalis supervenes the mortality may approach 95%. In many series, the outcome for fetuses with bilateral effusions and or associated polyhydramnios tend to have a poorer prognosis. There have been numerous reports of the benefit of aspirating these effusions in utero. The major difficulty is that they often reoccur quite readily and numerous attempts will be necessary. Drainage immediately prior to delivery is often beneficial, particulary when the effusions are quite large.

A recent review by Aubard et al analyzed the literature from 1977 to 1996 with regards to prenatally diagnosed cases of primary fetal hydrothorax. From 64 articles describing 204 cases they focused on 11 criteria. They additionally investigated those prognostic factors in the 89 cases where no in utero treatment was performed. They found 4 factors which correlated with the course of primary fetal hydrothorax; the presence of hydrops, the gestational age at the time of birth, whether the effusion was unilateral or bilateral and the occurrence of spontaneous resolution. With multivariate analysis, only hydrops remained determinant as a prognostic factor.

Of 108 cases where the reason for performing the study was stated, 63 were for a workup of polyhydramnios (58%), 40 were systematic (37%) and 5 were for another pathology. 75% of cases were discovered in the 3rd trimester. Primary fetal hydrothorax occurred most often bilaterally (74%). More than 50% of the time it was associated with hydrops. In 22% of cases spontaneous resolution occur ed (this occur ed in the face of large effusions and hydrops). Polyhydramnios most often occurs when the primary fetal hydrothorax is bilateral (79%). Overall fetal mortality for primary fetal hydrothorax was 34.8% of which 25% of deaths were in utero and 75% occurred postnatally. Of the 89 cases with no in utero treatment, the overall mortality was 39%. Only four criteria were found to have an adverse prognostic value: the bilaterality of the effusion, the presence of hydrops, the absence of spontaneous resolution and premature delivery. "Prior to 32 weeks, the results in the reported literature suggest that the greatest fetal survival can be obtained by placing of a pleuroamniotic shunt".

Differential Diagnosis: The major differential diagnosis are cystic or fluid filled collections within the thorax which simulate pleural fluid. These include: congenital diaphragmatic hernia, cystic adenomatoid malformation, bronchogenic cyst and pericardial fluid.

References:

Longaker MT, Laberge JM, Cansereau J, Langer J et al. Primary fetal hydrothorax: Natural history and management. J Pediatric Surgery 24:573-576, 1989

Hagay Z, Reece A, Roberts A and Hobbns JC. Isolated fetal pleural effusion: A prenatal management dilemma. Obstet Gynecol 81:147-152, 1993

Estroff JA, Parad RB, Frigoletto FD and Benacerraf BR. The natural history of isolated fetal hydrothorax. Ultrasound Obstet Gynecol. 2:162-165, 1992

Nicolaides KH, Azar GB Thoraco-amniotic shunting Fetal Diagn Ther 5:153-154, 1990

Gonen R, Degani S, Shapiro I, Samberg I and Sharf M. The effect of drainage of fetal chylothorax on cardiac and blood vessel hemodynamics J Clin Ultrasound 21:265-268, 1993

Castillo RA, Devoe LD, Falls G, Holzman GB et al. Pleural effusions and pulmonary hypoplasia. Am J Obstet Gynecol 157:1252-1255, 1987

Pijpers L, Reuss A, Stewart PA and Wladmiroff JW. Nonivasive management of isolated bilateral fetal hydrothorax. Am J Obstet Gynecol 161:330-332, 1989

Aubard Y, Derouineau I, Aubard V, Chalifour V, Preux P- M. Primary Fetal Hydrothorax: A Literature Review and Proposed Antenatal Clinical Strategy Fetal Diagn Ther 13:325-333, 1998

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Peter W. Callen, M.D.
Professor of Radiology, Obstetrics, Gynecology and Reproductive Science
University of California Medical Center, San Francisco, California