Fluid in Anterior or Posterior Cul-de-Sac

What a Finding of Free Fluid May Mean

The cul-de-sac is a small pouch in the female pelvis. Courtesy of Wikipedia Commons at http://en.wikipedia.org/wiki/Rectouterine_pouch.

Has your gynecologist or fertility specialist told you that you have fluid in your cul-de-sac area? Ultrasound can detect free fluid in the cul-de-sac, the area just behind the vagina. Learn the different causes and concerns about this finding.

Location of the Cul-de-Sac

There are two small pouches close to the uterus, one on either side, called the cul-de-sacs. Another term for cul-de-sacs is Pouch of Douglas, named after the Scottish anatomist James Douglas.


The anterior cul-de-sac is located between the bladder and the uterus. The posterior cul-de-sac is found between the uterus and the rectum. They are also called the excavatio recto-uterina (posterior) and excavatio vesico-uterina (anterior).

Finding Fluid in the Cul-de-Sac in Fertility Treatment

In women undergoing fertility treatment, fluid in the cul-de-sac (as seen on ultrasound) is a common finding in ovarian hyperstimulation syndrome (OHSS). If the doctor suspects that you have this condition, he will likely suggest that you have an ultrasound to check for fluid and measure your ovaries, as enlarged ovaries are also common in OHSS. Usually, fluid in the cul-de-sac is not a cause for alarm but could be causing discomfort and affecting your fertility.

Causes of Fluid in Cul-de-Sac

Fluid in the cul-de-sac can be caused by many different factors. Sometimes fluid from a ruptured cyst or follicle can accumulate there.

At other times, fluid in the cul-de-sac could indicate more severe problems. Here are some possible causes of fluid in the cul-de-sac:

  • Retrograde menstruation
  • Increased ovarian permeability due to estrogen influence
  • Uterine fibroids
  • Endometriosis
  • Ectopic pregnancy
  • Uterine rupture
  • Ovarian torsion
  • Pelvic inflammatory disease
  • Tubo-ovarian abscess
  • Pelvic abscess or hematoma
  • Gross ascites
  • Following culdocentesis
  • Hydatiform mole

Diagnostic Testing of Free Fluid in the Cul-de-Sac

Transvaginal ultrasound is the procedure that is used to show whether there is fluid behind the uterus. Fluid will show up well on ultrasound. If fluid is found in your cul-de-sac and you are experiencing pain, your doctor may order more advanced testing of the fluid.

Culdocentesis is a procedure performed to check any abnormal fluid in the cul-de-sac area. Before transvaginal ultrasound became widely available, it was also used to detect the fluid. Now, it is used to remove fluid to evaluate.

This procedure involves inserting a needle through the vaginal wall to draw off a sample of fluid to analyze. A numbing agent or anesthesia may be used prior to the procedure. You will have a pelvic exam and your health care provider will hold the cervix with an instrument to insert the needle in the correct place.

A small amount of fluid is normal and is usually not of concern. If the fluid sample shows signs of pus or blood, the area may need to be drained. Sometimes blood can be a result of ruptured cyst or signs of an ectopic pregnancy. The presence of pus could indicate an infection caused by a tear or other conditions.

The blood would need to be drained and antibiotics used to treat the infection.


Culdocentesis. MedlinePlus. https://medlineplus.gov/ency/article/003919.htm.

Focus On - Ultrasound Imaging in First Trimester Pregnancy. American College of Emergency Physicians. https://www.acep.org/Clinical---Practice-Management/Focus-On---Ultrasound-Imaging-in-First-Trimester-Pregnancy/.