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ULTRASOUND OF
CIRCUMVALLATE PLACENTA |
Two phases have been described by Bey (1) and co-workers:
- Active Phase.
- Infolding of fetal membranes towards the fetal surface of the placenta.
- Passive Phase.
- Bright border at the periphery of the placenta.
- Occurs after the one-fourth ratio of fetal sac to placenta is reached.
- Anatomically the border may represent the fibrosed, infolded membrane.
- Anechoic subamniotic cystic areas (2).
- Marginal diffuse "mamelonnated" chorionic plate (fetal surface), which has the appearance of anechoic subamniotic cystic spaces. This is the main sonographic feature of circumvallate placenta, and represents multiple subamniotic echo-free areas of various sizes and shapes (*). They are limited to the marginal zone of the placenta and persist throughout pregnancy.
- Irregular rolled-up edges of the placental membranes (contain amnion, chorion and decidual tissue) (**).
- Progressive fibrin deposition, especially during the third trimester, may result in the area becoming more echogenic (2).
- Subchorionic echo poor marginal areas (2) corresponding to marginal deciduous hematomas.
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Video clip of Circumvallate Placenta
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COMPLICATIONS |
As
the uterine wall stretches during the second half of pregnancy, the placenta
cannot adapt and there is tearing of the membranes and bleeding from the edge
of the chorionic plate. There is therefore a
relatively high rate of premature rupture of membranes, antepartum
bleeding and premature onset of labour.
DIFFERENTIAL DIAGNOSIS |
- Subamniotic cyst and hematoma are often solitary, central and well delineated (2).
- Subchorionic thrombosis or fibrin deposition is found in ± 20% of normal placentas at delivery.
REFERENCES |
- Bey M, Dott A, Miller JM. The sonographic diagnosis of circumvallate placenta. Obstetrics and Gynecology 1991;78(3):515-516.
- Jauniaux E, Avni FE, Donner C et.al. Ultrasonographic diagnosis and morphological study of placenta circumvallate. J Clin Ultrasound 1989;17:126-131.