* Ultrasound Division, ASL Roma B, Rome, Italy.
** Gynecology Department, Nuova Villa Claudia, Rome, Italy.
*** Ultrasound Division, Ceprano Hospital, Ceprano, Italy.
Introduction
Subamniotic hematomas result from the rupture of chorionic (fetal) vessels close the umbilical cord insertion[1]. There are most often found near the placental cord insertion under the thin amniotic layer covering the chorionic plate and protrude into the amniotic cavity. There occur as a single or multiple findings. They don't show any blood flow on Color Doppler. They may rupture into the amniotic cavity resulting in blood stained hyperechoic amniotic fluid. When reabsorbed, subamniotic bleeds may present as an hyperechoic deposits on the fetal surface of the placenta.
Associated intrauterine growth restriction has been reported in approximately 10% of cases. More than 3 cysts or cysts larger than 4.5 cm are more frequently associated with intrauterine growth restriction [2].
Sonographic findings show the mass protruding from the chorionic plate into the amniotic cavity. Echotexture of the recent subamniotic hematoma is similar to a solid mass. Chronic subamniotic hematoma has an appearance of predominantly cystic mass [3]. The latter contains an hyperechoic component attached to the fetal surface of the placenta, representing a retracted blood clot and/or a fibrin deposit.
The main differential diagnosis includes placental cyst and a large umbilical cord cyst near at the placental insertion. True placental cysts (cytotrophoblastic cysts) may be found within the placenta itself or under the fetal plate, but they contain a gelatinous material rather than blood and are not associated with poor perinatal outcome. In the case of a cord cyst, the structure is anechoic and lacks a hyperechoic, solid component. More than 20% of umbilical cord cysts in the first trimester are associated with fetal chromosomal abnormalities or structural defects, especially when located close to the placental insertion [4].
Case report
A 38-year-old G2P1 was referred to our department at 35 weeks of gestation for the suspicious of a umbilical cord cyst. Patient underwent an amniocentesis at 17 weeks of gestation with a normal result, karyotype 46,XY. Previous ultrasound exams at 12 and 21 weeks of gestation were reported as normal.
Ultrasound examination showed a normal fetal growth and no evidence of fetal anomalies. The umbilical vein was slightly dilated (11 mm) in its intraabdominal extrahepatic portion. The placenta was located anteriorly and had a normal echotexture. The previously described cystic mass measured 67x64x44 mm (larger than in the previous examination). It was seen to protrude from the fetal surface of the placenta into the amniotic cavity and was covered by the thin amniotic layer. Cyst contained a hyperechoic avascular structure measuring 23x17 mm and arising from the chorionic plate. The cyst was localized in close proximity of the placental cord insertion but there was no continuity between the cord and the cyst. Umbilical cord Doppler performed in the cord portion near the cyst was normal. The amount of the amniotic fluid was in the upper limits for the gestational age (AFI 22 cm). This is often found in cases of subamniotic cysts, maybe due to transudation through the cyst walls.
A healthy neonate was born spontaneously at 39 weeks of gestation, 4100 grams/51 cm.
The placenta was large and the cyst was covered by the amniotic membrane and was visible on the fetal side of the placenta.
Pathological examination of the placenta confirmed a cystic structure arising from the amniotic membrane, subamniotic cyst. The hyperechoic area within the cyst corresponded with an organized thrombus. The rest of the placenta was normal.
Images 1,2: 35 weeks, Image 1 shows a proximity of the cyst to the umbilical cord insertion. Image 2 shows an hyperechoic structure within the cyst.