What is endometriosis?

Female Reproductive System

Endometriosis is a common condition. The tissue that normally lines the uterus (also called the endometrium) is found in sites outside the uterus. This misplaced tissue is commonly found on the ovaries or the tissue lining the pelvis (peritoneum), however it may also be found on the uterus, bowel, bladder, utero-sacral ligaments (bands of tissue at the back of the uterus that hold the uterus in place) and in the Pouch of Douglas (the area between the uterus and the bowel).

The misplaced tissue implants itself onto the surface of the tissue or organ where it has been deposited and begins to grow and function. These implants (also known as patches or deposits) respond to the hormones of the menstrual cycle in the same way as does the lining of the uterus (endometrium). Like the endometrium, the implants thicken and swell with blood in order to prepare for a possible pregnancy. If a pregnancy does not occur then both the endometrium and the implants break down and bleed (the period). Unlike the lining of the uterus, the blood from the implants cannot escape from the body during a period, so it bleeds directly onto the surface of the surrounding organs and tissues. This causes irritation which leads to inflammation, scarring and, sometimes, the development of adhesions between organs so that they stick together. On the ovary, the patches can increase in size and burrow in to form cysts, known as chocolate cysts or endometriomas.

Unlike the lining of the uterus, the blood from the implants cannot escape from the body during a period, so it bleeds directly onto the surface of the surrounding organs and tissues.  This causes irritation which leads to inflammation, scarring and, sometimes, the development of adhesions between organs so that they stick together. On the ovary, the patches can increase in size and burrow in to form cysts, known as chocolate cysts or endometriomas.

How common is endometriosis?

Endometriosis is thought to affect approximately 10 per cent of women (one in 10) at some stage during their menstruating years. It can occur anytime, from when periods start, right up to the time of menopause. It rarely continues to be active after menopause but occasionally, may be reactivated by hormone therapy after menopause. In rare cases, endometriosis may develop into cancer.

Endometriosis can have a major impact on quality of life with the symptoms interfering with work, relationships, family and overall health. One of the main issues is that there is often a delay in diagnosing endometriosis and some women have symptoms for many years before treatment is started.

What causes endometriosis?

The causes of endometriosis are not fully understood and there may be many reasons why it occurs in about 10 per cent of women. Potential causes include genetics, especially if there are other family members with the condition, problems with the immune system and possibly environmental toxins (yet to be proven). Retrograde menstruation is considered the main source of endometrial cells reaching the pelvis and pelvic organs.

Retrograde menstruation is when lining cells from the uterus, which are normally shed during the period, flow back along the uterine (Fallopian) tubes into the pelvis where they become implanted and begin to grow.

This theory could explain why implants are most commonly found on the ovaries, or near the end on the uterine (Fallopian) tubes. However, it does not explain cases where endometrial cells are found outside the pelvic cavity.

Content Updated July 31, 2009