Placenta circumvallata

Circumvallate placenta refers to a variation in placental morphology in which, as a result of a small chorionic plate, the amnion and chorion fetal membranes ‘double back’ around the edge of the placenta.

Epidemiology

The prevalence is estimated to be around 1-7% .

Pathology

There is an inward insertion of membranes from the edge towards the center of the placenta (from deep implantation of the placenta into the decidua). Because of this excessive implantation, the placenta covers more than half of the fetal sac. The placenta reduces this excessive covering to the normal one-fourth by separating from the uterine wall, with the resultant back folding of the placenta and fetal membranes towards the chorionic surface.

This can be accompanied by tethering of membranes, frequently in association with a marginal infarction, hemorrhage, or fibrin deposition.

Radiographic features

Antenatal ultrasound

May show a peripheral rim of chorionic tissue appearing as an echodense ridge (placental shelf) .

On 3D ultrasound, it has an appearance similar to a tire (the "tire sign").

Treatment and prognosis

Recognized complications include :

• higher incidence of placental abruption 
• increased risk of IUGR

Differential diagnosis

For a raised placental edge on ultrasound:

• amniotic shelf (amniotic sheet)
• part of an amniotic band close to the placenta

Siehe auch:

• Amniotisches-Band-Syndrom
• Placenta extrachorialis
• Entwicklungsanomalien der Plazenta
• Placenta circummarginata
• Amnionblatt

und weiter:

• obstetric curriculum
• placenta
• variation in placental morphology