Pseudogestational sac

Dr Craig Hacking and A.Prof Frank Gaillard et al.

A pseudogestational sac or pseudosac 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 endovaginal ultrasound imaging and caution should be exercised if considering diagnosing a pseudogestational sac with modern ultrasound equipment. In a woman with a postive 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
  • 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 intra-decidual sign, which is also a sign of an early pregnancy.

The idea of beta-hCG "discriminatory levels" has also undergone revision since this sign was formulated. Caution should be exercised in making a diagnosis of pseudogestational sac because an intrauterine fluid collection does not show a yolk sac at a beta-HCG level >2000 7. Therapy should not be initiated in a hemodynamically stable woman on the basis of a single beta-hCG level.

Differential diagnosis

Ultrasound - obstetric
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Article information

rID: 1931
System: Obstetrics
Section: Signs
Synonyms or Alternate Spellings:
  • Decidual cyst
  • Pseudo-gestational sac
  • pseudosac

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Cases and figures

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    Case 1: Pseudogestational sac
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