Imaging description

A pseudogestational sac (also known as a pseudosac) presents as an oval fluid collection centrally located within the uterine cavity of a pregnant patient.

The earliest sign of an intrauterine pregnancy (IUP) is the intradecidual sign, a small fluid collection surrounded by an echogenic ring, eccentrically located within the endometrium (Figure 72.1) [1].

Soon after, a double decidual sac sign may be identified, which is a small eccentric fluid collection within the endometrium, partially surrounded by two layers of decidua.

In contrast, a pseudosac consists of fluid located centrally within the uterine cavity (not within the endometrium), and surrounded by only one layer of decidualized endometrium (Figure 72.2). A double decidual sac sign is absent [2, 3]. “Beaking” of the fluid collection is suggestive of a pseudosac, but a leiomyoma or focal uterine contraction can cause a similar appearance in an IUP [4].

Decidual cysts are thin-walled cysts, usually at the junction of the endometrium and myometrium. They are non-specific findings and are identified in non-pregnant patients, normal IUPs, and ectopic pregnancies [1].

Although the intradecidual and double decidual signs have been reported as accurate, if there is any question about the location of the fluid, it is prudent to take a more conservative approach and specify that findings could represent an early IUP or a pseudosac associated with ectopic pregnancy, to ensure that an ectopic pregnancy diagnosis is not missed, resulting in a potentially fatal outcome.