Fluid in Anterior or Posterior Cul-de-Sac

Your gynecologist or fertility specialist may report that an ultrasound has detected free fluid in your cul-de-sac area. This is an area just behind the vagina. Learn the different causes and concerns about this finding.

Cul-de-Sac Anatomy

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

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:

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

Finding 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 your doctor suspects that you have this condition, they 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.

Diagnostic Testing

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.

A small amount of fluid in the cul-de-sac 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.