Circumvallate placenta vs. Uterine synechiae vs. Amniotic sheet

[Linh]

Dear Steve,

I have recently come across a Nuchal with a band going across the left portion of the placenta that looks like a sheft sign (2 clips below).

The radiologist described it as: Amniotic sheet only contacting the placental edge superiorly but may be incomplete. No foetal involvement => Fetal medicine unit referral for further clarification.

I was wondering how you can differentiate the 3 entities: circumvallate placenta, uterine synechiae and a normal amniotic sheet.

I know that in Amniotic band syndrome fetal parts are entangled and constricted by the amniotic band, but when it is ambiguous in this case, it is hard not to worry the patient as we tend to be overcalling just in case.

Best regards,
Linh

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[Stephen Bird]

Hi Linh,

This is a good question.

Personally I think your example is a synechiae causing an amniotic sheet.

A synechiae is just an adhesion across the endometrial cavity and if they are multiple it is Ashermans syndrome.
When the gestational sac forms the adhesions cause this appearance as the amnion and the chorion must wrap around them essentially causing 4 layers of membrane hence the thick “band” appearance.

I think of these as exactly the same thing as an amniotic shelf.

Circumvallate placenta is different where the implantation site is too small for the placenta mass in simple terms and hence the membranes are puckered and protrude forward at the edge of the placenta.

Amniotic band syndrome is completely different again and this indeed causes limb deformaties. The limb issues occur due to the fetus coming in contact with the back surface of the amnion (the edge that is normally against the chorion) So this requires a perforation of the amnion and the floating membrane is really thin and whispy, not like your example.

So I think yours will just be a shelf caused by a synechiae and will be nothing to worry about.

Let me know what the tertiary referral folk think!

Steve.

[Linh]

Hi Steve,

Thanks for your detailed reply.

In retrospect, I do think it was just a benign finding of a uterine synechiae as the band does not necessarily follow the placental edges like that shelf sign from circumvallate placenta. But is it something to document as it may change management? Would a synechiae potentially complicate a pregnancy?

I’ll let you know if they come back for another scan.

Best regards,
Linh

[Stephen Bird]

I don’t think there will be any issues here,

It is worth documenting as it may potentially change the method of delivery.

Steve.

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