Pseudogestational sac

A pseudogestational sac, also known as a pseudosac or intra-cavitary fluid, is the concept that a small amount of intrauterine fluid in the setting of a positive pregnancy test and abdominal pain could be erroneously interpreted as a true gestational sac in ectopic pregnancy.

The sign was originally reported before the use of transvaginal ultrasound imaging and caution should be exercised if considering diagnosing a pseudogestational sac with modern ultrasound equipment. In a woman with a positive beta-hCG, any intrauterine sac-like fluid collection seen on ultrasound is highly likely to be a gestational sac ⁶.

Radiographic features

Ultrasound

• generally irregularly-shaped with pointed edges and/or filled with debris, sometimes referred to as 'beaking'
• centrally located in the endometrial cavity, rather than eccentrically located within the endometrium
• displaces the anterior and posterior endometrial cavity surfaces
• does not demonstrate a yolk sac
• a double decidual layer is compatible with intrauterine pregnancy, but lack of this sign is not specific for pseudogestational sac
  • may be surrounded by a thick decidual layer

It should be distinguished from an intradecidual sign, which is also a sign of early pregnancy.

The idea of beta-hCG "discriminatory levels" has also fallen out of favor since this sign was formulated. Caution should be exercised in making a diagnosis of pseudogestational sac based on a beta-HCG level at which a yolk sac is expected to be seen as this has been shown to be unreliable.  Therapy should not be initiated in a haemodynamically-stable woman on the basis of a single beta-hCG level.

Differential diagnosis

• decidual cyst
• normal intrauterine pregnancy
• anembryonic pregnancy
• incomplete miscarriage
• blood products