Fetal Medicine Center, Department of Obstetrics and Gynecology, Clinica Las Condes, Santiago, Chile

Case report

A 26-year-old primigravida was referred to our unit at 25 weeks' gestation because of the detection of an intra-amniotic cystic mass thought to represent an umbilical cord cyst. Sonographic evaluation demonstrated a singleton fetus in vertex presentation with measurements consistent with dates. The placenta was posteriorly located, the amniotic fluid volume was normal, and the umbilical cord had three vessels. A non-tense, cystic mass measuring 50x33 mm was seen protruding from the fetal surface of the placenta and close to the placental cord insertion. In addition, there was an elongated, echoic structure within the cyst, which was noted to be attached to the surface of the placenta. An umbilical cord cyst was ruled out because careful examination of the whole length of the cord failed to demonstrate a close connection between the cord and the cyst. Color Doppler sonography ruled out blood flow within the mass and there were normal blood flow velocity waveforms in the umbilical cord.

Discussion

Subamniotic hematomas result from the rupture of chorionic vessels near the cord insertion (1). Only few cases prenatally diagnosed by sonography have been reported (1,2,3), and our case seems to be the first in which 3-D ultrasound evaluation is available. The prenatal sonographic features in chronic subamniotic hematomas are characteristics and include the detection of a cystic mass overlying the fetal plate of the placenta and covered by a thin membrane (the amnion), together with the identification of an echoic mass attached to the fetal placental surface representing the retracted clot (1,2). The main differential diagnosis is a Placental cyst, but in this condition the cyst is clear and lacks of an echoic mass within. In recently developed hematomas, however, the mass can be entirely echoic and must be differentiated from a placental chorioangioma by the use of color flow imaging (3). Subamniotic hematomas have been associated to increased maternal serum AFP levels, vaginal bleeding, suboptimal fetal growth, and polyhydramnios. Therefore, a close surveillance for these potential complications is advised.

References

1.      Deans A, Jauniaux E. Prenatal diagnosis and outcome of subamniotic hematomas. Ultrasound Obestet Gynecol 1998;11:319-23.

2.      Van der Bosch T, Van Schoubroeck D, Cornelio A, et al. Prenatal diagnosis of a subamniotic hematoma. Fetal Diagn Ther 2000;15:32-5.

3.      Sepulveda W, Aviles G, Carstens E, et al. Prenatal diagnosis of solid placental masses: the value of color flow imaging. Ultrasound Obstet Gynecol 2000;16:554-8.