Category: 4. Free Fluid Evaluation with Pelvic Ultrasound

There are several pathologic conditions (both pelvic and non-pelvic) associated with an abnormal buildup of free fluid in the pelvis. 

Here is a list of potential pelvic causes of abnormal amounts of free fluid in the Pouch of Douglas:

• Endometriosis
• Malignancy
• Leiomyoma
• Pelvic Inflammatory Disease
• Ectopic Pregnancy

When you do see a significant amount of free fluid in the Pouch of Douglas make sure to check the right upper quadrant (RUQ) in Morison’s Pouch and the left upper quadrant (LUQ) to evaluate for more free fluid. Remember, free fluid can also be due to non-pelvic causes such as liver cirrhosis (alcohol-related or viral), heart failure, renal failure, and trauma. Below are ultrasound images of abdominal free fluid in the left and right upper quadrants.

Small amounts of free fluid in the pelvis (usually <10 mL but up to ~20 mL near ovulation) can be normal in females (Ritchie, 1986; Hall et al., 1979). This is especially true in patients following ovulation, after menopause, or during early pregnancy. Make sure to look for the free fluid in the Pouch of Douglas.

Here are some pelvic ultrasound images of normal amounts of free fluid in the pouch of Douglas.

Free fluid is one of the most common findings during pelvic ultrasound. A variety of abdominal and pelvic conditions are associated with free fluid accumulation in the pelvis.

In females, free fluid from the abdominal cavity sinks into the pelvic cavity and settles in the Pouch of Douglas (also called the Posterior Cul-De-Sac and Rectouterine Pouch), located posterior to the uterus and anterior to the rectum. Anechoic fluid in this location can be detected by ultrasound imaging using either the transabdominal or transvaginal approaches.