Differential diagnosis of free fluid in cul de sac (pouch of Douglas)

Last revised by Daniel J Bell on 20 Sep 2019

The cul-de-sac, also known as the pouch of Douglas or rectouterine pouch, is an extension of the postero-inferior reflection of the peritoneal fold between the uterus (anteriorly) and rectum (posteriorly). It is the most inferior aspect of the peritoneal cavity and therefore the first location where free fluid accumulates.



Presence of fluid within the cul-de-sac is a common finding, and the underlying cause can be thought of as either physiological or pathological. 


Physiological pelvic intraperitoneal fluid in women may be due to:

  • ruptured follicles
  • retrograde menstruation
  • increase in ovarian permeability due to estrogen influence

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