The pouch of Douglas is an anatomical structure named after the Scottish anatomist James Douglas. It is a bag-shaped extension of the peritoneum (a membrane that lines the insides of the abdomen and pelvis) located between the posterior wall of the uterus and the rectum. It is found in females. In males, the corresponding rectovesical pouch is found between the rectum and bladder.

Since it extends from the peritoneum, it is lined by peritoneum that arises from the Mullerian system that is not involved in the embryonic development phase known as organogenesis.

Women of childbearing age will show about 1 mL to 3 mL of fluid in the pouch of Douglas during their menstrual cycle. The quantity increases slightly following ovulation (4 mL to 5 mL).

Some of the other names for pouch of Douglas include the following:

Rectouterine pouch.
Cul-de-sac.
Rectovaginal pouch.
Rectouterine excavation.
Uterorectal pouch.
Douglas space.
Douglas cavity.
Douglas pouch.
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Douglas cul-de-sac.
Cavum Douglasi.
Ehrhardt–Cole cul-de-sac.
Ehrhardt–Cole recess.
Excavatio rectouterina.

The rectouterine pouch is the most dependent part or area of the peritoneal cavity.

What Are the Anatomical Boundaries of the Pouch of Douglas?

The anatomical boundaries of the pouch of Douglas are as follows:

Anterior: Uterus, posterior fornix of the vagina.
Posterior: Rectum.
Inferior: Peritoneal rectovaginal fold.

What Pathological Issues Can Arise in Relation to the Pouch of Douglas?

1. The collection of fluids in the pouch of Douglas is a possible pathological phenomenon. This is especially possible when the female is lying in the supine position. Since the rectouterine pouch is the most dependent part of the peritoneal cavity, found in the lower areas, it is easy for fluids to collect in this area. The fluids typically arise from infectious or diseased circumstances or conditions such as abscesses, intraperitoneal drop metastases, ascites, hemoperitoneum, and infections. While a small amount of low-attenuated (less intense) and homogeneous fluid is to be expected in the rectovaginal pouch of most child-bearing women of reproductive potential, it is considered a pathological condition when there is excessive or infectious fluid.

2. Primary malignancies, although extremely rare, may also occur in the pouch of Douglas.

Mass-like lesions that arise in the pouch of Douglas may often prove quite challenging for healthcare providers due to the possibility of misdiagnosing these masses as tumors arising from the uterus or adnexa (the region adjoining and around the uterus that contains the uterus, fallopian tubes, and all associated connective tissue, vessels, and ligaments).

Most malignancies associated with the pouch of Douglas have been Mullerian-type malignancies. Mullerian adenosarcomas are mixed tumors comprising benign and malignant components. These components arise from the uterus. Adenosarcoma in the pouch of Douglas are extremely rare and the known cases have demonstrated varying degrees of severity. While adenosarcoma are usually benign, some variants may present in a malignant and aggressive manner. Pouch of Douglas adenosarcoma may be accompanied by endometriosis in some cases, but most of these cases have been successfully treated, with a disease-free prognosis.

[Endometriosis: A painful condition where tissue similar to the endometrium (tissue lining the uterus) grows outside the uterus. It generally affects the ovaries, pelvis, and fallopian tubes and may result in pain and irregular menstruation].

Carcinosarcomas are aggressive tumors that should be watched out for but are quite rare in association with the pouch of Douglas lesions. When these do occur, patients may require equally aggressive therapy options. Unfortunately, most reported cases have ended with mortality.

What Are the Fluids That May Collect in the Pouch of Douglas and Their Causes?

1. Physiological: The fluids that collect regularly during the menstrual cycle are the following:

Menstrual blood that may have refluxed through the fallopian tubes.
Fluids produced during ovulation.

2. Pathological: The fluids that may collect due to other pathological causes include the following:

Fluids related to ruptured cysts.
Blood from ruptured ectopic pregnancies.
Ascites (fluid buildup in the abdomen) due to liver failure, cardiac failure, or malignancies.
Inflammatory debris arising from an infection of the pelvis or appendix.

What Are the Symptoms of Pouch of Douglas Malignancies?

Abdominal pain.
Abdominal distension (abnormal outward swelling or bloating of the abdomen).
Presence of a lump at the introitus (the opening of the vagina that leads into the vaginal canal).
Reduced caliber of stool (thin or narrow stools).
Abnormal bleeding of the uterus.

How Is the Pouch of Douglas Evaluated?

A physical evaluation is the first step in the evaluation of pathological conditions in the pouch of Douglas. This is followed up with imaging modalities that may range from pelvic ultrasounds to magnetic resonance imaging (MRI) modalities. These are typically used when checking for malignancies.

Pelvic ultrasound is the preferred modality when viewing pelvic masses as there is no requirement for a contrast medium, and it is an inexpensive technique.

MRI is preferred when the lesions present require better characterization or soft tissue delineation to allow for a detailed and thorough surgical plan.

What Are the Treatment Options for Pouch of Douglas Pathologies?

1. Surgery: Surgery may be indicated for the following pathologies associated with the rectouterine pouch:

Endometriosis.
Abscess in the rectouterine area or pouch.
Rectouterine hernia.
Malignancies.

The preferred surgical treatment in most cases is keyhole technology-based minimally invasive surgery.

2. In some cases, fluid aspiration via a puncture may be the only procedure that is required.

3. Most malignancies of the pouch of Douglas may require primary surgery with adjuvant therapy.

What Are the Uses of the Pouch of Douglas?

The pouch of Douglas is a good site for peritoneal dialysis, making it invaluable in patients with end-stage renal failure. A catheter called the Tenckhoff catheter is placed in the pouch (specifically the distal end) and may even be sutured to the bladder. This helps prevent the migration of the bladder.

Conclusion:

By itself, the pouch of Douglas is simply an anatomical structure that displays some fluid collection throughout the course of a woman’s menstrual cycle (or during her childbearing years). However, it should be noted that the pouch of Douglas is a central area or location for seeded lesions due to its dependency when upright or supine. Most cases of pouch of Douglas pathologies are treatable, and malignancies occur very rarely, making this an area of interest but not a cause for excessive concern.