Fluid in Anterior or Posterior Cul-de-Sac

If you've had an ultrasound, you may have learned that there's fluid in your cul-de-sac area. The cul-de-sac sits just behind the vagina.

This article explains why fluid can sometimes collect there, and how your healthcare provider might diagnose the reason for it.

Anatomy

On either side of the uterus sit two small pouches. These are called the cul-de-sacs. The anterior cul-de-sac is the space between the bladder and the uterus. The posterior cul-de-sac is between the uterus and the rectum. This latter cul-de-sac is also known as the pouch of Douglas, named for the Scottish physician James Douglas. 

Causes

Fluid can fill the cul-de-sac for many reasons. Sometimes a ruptured ovarian cyst or follicle leaks fluid. Sometimes there's a more severe problem. Here are some possible causes:

• Ectopic pregnancy, where a pregnancy grows in a fallopian tube instead of the uterus
• Endometriosis, when the type of tissue that normally lines the uterus grows somewhere else
• Following culdocentesis, a procedure to remove fluid from the pouch
• Gross ascites, which is fluid buildup in your abdomen
• Hydatidiform mole, also known as a molar pregnancy, where a cyst forms from a fertilized egg
• High doses of estrogen causing fluid to leak out of blood vessels
• Ovarian torsion, where the fallopian tube and ovary twist
• Pelvic abscess or hematoma, a pocket of infected fluid or blood
• Pelvic inflammatory disease
• Retrograde menstruation, when your period flows back into your pelvis
• Tubo-ovarian abscess, a pus-filled area in your ovary and fallopian tube
• Uterine fibroids, growths in the uterus that are not cancerous
• A tear or break in the uterine wall

Fertility Treatment

If you are having fertility treatment, fluid in the cul-de-sac can be a symptom of ovarian hyperstimulation syndrome (OHSS). That's a condition where high doses of fertility hormones make your ovaries swell.

If your healthcare provider suspects that you have OHSS, they may suggest an ultrasound to check for fluid. During the ultrasound, they can measure your ovaries.

Usually, fluid in the cul-de-sac is not a cause for alarm. In some cases, though, it can cause discomfort or affect your fertility.

Diagnosis

A transvaginal ultrasound will show whether there is fluid behind the uterus. This is a test in which a wand is placed into the vagina to take more detailed ultrasound images. If fluid is found and you are having pain, you may need more tests.

One way to test for fluid is with culdocentesis. Before transvaginal ultrasound became widely available, this procedure was used to check for fluid in this area. Now, it is used to remove a fluid sample for testing.

A small amount of fluid in the cul-de-sac is normal. But if the sample shows signs of pus or blood, the area may need to be drained.

Blood in the fluid could mean a cyst has ruptured or there is a tear. It could also be a sign of an ectopic pregnancy. Pus could mean you have an infection. Your healthcare provider may prescribe antibiotics for the infection.

Summary

Two small pouches called cul-de-sacs are located on either side of the uterus. Fluid sometimes builds up in these pouches. A little fluid is normal, but if it contains pus or blood, or if it's causing pain, there may be a bigger health problem.

Infection, pregnancy complications, or health conditions such as endometriosis or fibroids could be the cause. It's also possible that a cyst, a follicle, or the uterus itself has ruptured. In some cases, fertility treatment can cause the extra fluid.

An ultrasound can usually detect the fluid. You may also need a culdocentesis, where a sample of the fluid is drawn out with a needle so it can be tested. Depending on the cause, the fluid may need to be drained or treated with antibiotics.