Pitfalls and Practical Challenges in Sonographic Imaging of the Uterus

Cesarean Scar Pregnancy

Now what about this case?

Positive beta. First trimester empty endometrium
and we see a mass in the lower uterine segment.
What is your differential diagnosis?

Could it be a cesarean scar ectopic
or scar ectopic as we call it?
Is it a cervical ectopic or could it be an ongoing SAB?
What do we look for?

A scar ectopic is a cesarean scar pregnancy.
Before 2002, only 19 cases were reported.
Estimate one in 2,230
to one in 10,000 of all pregnancies.
The rate is 0.15% in women with a prior C-section
and accounts for 6%
of all ectopics in women with prior C-section.

Some say it's different from accreta in
that it has an absent myometrium between the bladder
and the gestational sac,
but this is not always easy to distinguish.

So the differential diagnosis includes
spontaneous abortion in progress.
Cervical ectopic pregnancy and a scar ectopic.

Kovic has described criteria in 2003
of having an empty endometrial cavity,
a gestational sac located anteriorly at the level
of the internal os, covering the site
of the prior C-section.
Scar evidence of functional placental trophoblastic,
circulation on doppler and no sliding sign.

Here's the same case.
We see that there is one of the signs here.
The gestational sac is located anteriorly at the level
of the internal os covering the site
of the prior C-section site.
The uterus is empty on color doppler.
There's evidence of functional trophoblastic disease
with vigorous flow surrounding the mass.
There's also bulging outside of the cervix
as we see in the lower portion of this image.
And on M mode.
This one even had a heartbeat, which
demonstrated a live ectopic pregnancy.

This patient went to MRI.
We see that the fundal endometrium,
the whole endometrium actually is empty.
We see this heterogeneous mass obscuring the cervix.
Here's part of the posterior cervix.
The anterior is not even seen.
It's effacing the bladder wall.
And this patient went to embolization pre embolization.
Here is the vigorous flow in the region
of the cervical ectopic post embolization.
We see there's virtually no flow in this region at surgery.
Here is the cervical ectopic.
Here is the anterior uterus,
the cervical ectopic bulging outward,
which popped out easily according to the surgeon,
and there was successful repair of the anterior cervix.

So in our hands, you can't always immediately distinguish
by imaging a scar ectopic from placenta accreta,
especially if early in pregnancy
and even a cervical ectopic can appear similar if very
early in pregnancy.

Here we see a gestational sac insinuating into the
cesarean section scar.

Cervical Ectopic Pregnancy

Now what is this entity?
This appears a little bit different than the other.
So here we have an anterior and a posterior cervix.
This is a cervical ectopic pregnancy.
It accounts for less than 1% of all ectopic pregnancies.
The risks are multiparity, prior abortion,
prior instrumentation of the cervix of the endometrium.

The features are a gestational sac with a live embryo
or peritrophoblastic flow in the cervix.
If there is a gestational sac without live embryo,
then you have a different differential diagnosis.
Is it a cervical ectopic with a demise embryo
or an ongoing spontaneous abortion?

So we look for peritrophoblastic flow.
If there's peritrophoblastic flow, it's most likely going
to be a cervical ectopic implanted in the cervix.
We look for serial changes in the sac shape and position,
and that is the sliding sac sign
that would tell us it's a spontaneous abortion in progress.

What are the sonographic features?

The cervix is enlarged as we see here.
The uterine enlargement takes an hourglass shape also,
as we see here with a waist at the lower
cervical LUS junction.
There's no intrauterine pregnancy within the endometrium
and the placenta and entire chorionic sac must be
below the internal os
and the level of the uterine arteries.
The cervical canal should be dilated
and barrel shaped as we see here,
and we will not see a sliding sign, AKA.
This will not move in serial imaging of this cervix.

Here's the enlarged cervix, also barrel shaped.
Here is trophoblastic flow.
That tells us this gestational sac is
implanted in the cervix.
The uterus is hourglass shaped.
Better seen here with a waist at the lower uterine segment
slash cervical junction.

So you cannot always distinguish,
especially if early in pregnancy,
scar ectopic from placental invasion from cervical pregnancy.

Conclusion

So we have reviewed the common challenges in imaging,
the uterus, fibroids,
and eccentrically located gestational sacs.