Ectopic Pregnancy Part 2

When you do a sonogram on a woman who is suspected of harboring an ectopic pregnancy, the key observation is to see an intrauterine pregnancy, and whether you see that transabdominal or with endovaginal sonography.

Once you identify that there is an intrauterine pregnancy, that puts the woman at an extraordinarily low risk for an ectopic pregnancy because the concomitant occurrence of both an intrauterine and an extrauterine pregnancy, the so-called heterotopic pregnancy, is particularly uncommon.

It is exceptionally uncommon in women who do not have a risk factor. Those risk factors are usually assisted pregnancy, in vitro fertilization, and so on.

However, when we diagnose an intrauterine pregnancy, we want to make sure that we’re using very strict and reliable morphologic criteria. Among those, these four are reliable:

the double sac sign
identification of yolk sac
identification of an embryo
identification of an embryo with a heartbeat, which is key.

So reliability increases in this direction.

But unfortunately, early diagnosis increases in the opposite direction. So here you have a nice example of the two findings that are at the top of the list in terms of being able to see them early. One is an early yolk sac and the other is the double sac sign.

The double sac sign is characterized by two distinctly bright echogenic lines, which encompass a modest amount of the gestational sac.

The reason we must be so cautious to use strict criteria is because of an entity called the pseudogestation sac of ectopic pregnancy.

In a pseudogestation sac of ectopic pregnancy, you may well see a well-defined fluid collection surrounded by an echogenic rim inside of the uterus. That means that seeing an intrauterine fluid collection surrounded by a rind of bright echoes is an insufficient criterion to diagnose an intrauterine pregnancy.

So if we were to compare two fluid collections of equal size within the uterus, one clearly surrounded by two discreet rings of echoes, and the second one by one only, this latter one  we couldn’t diagnose as an intrauterine pregnancy. That is a pseudogestation sac of ectopic pregnancy.

Author: Roy A. Filly, MD
Excerpted from:
Diagnostic Imaging Review: For Residents, Fellows and Radiologists
Female Pelvis Section