Women's Health Matters

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Medical Description

The name endometriosis comes from the word endometrium. The endometrium is the tissue that lines the inside of the uterus. This tissue builds up every month and then sheds when a woman has her period. Sometimes tissue that is like endometrial tissue shows up on the outside of the uterus and in other places in the body, and starts to grow. This is called endometriosis.

Endometrial tissue (shown in green)
Endometrial tissue (shown in green) can attach to many of the pelvic organs.

The most common locations for endometrial growths are in the:

  • cul-de-sac, or pouch between the uterus and rectum
  • ligaments that attach the uterus and cervix to the base of the spine
  • ovaries
  • surface of the uterus
  • bowel
  • rectum
  • bladder
  • lining of the abdominal cavity (peritoneum)

Endometrial growths can develop in places outside the abdomen and pelvis, such as the lung, arm and thigh, although this is rare.

Clumps of endometrial tissue growing outside the uterus may be called nodules, lesions, implants, cysts or growths. Sometimes the cysts are called “chocolate cysts” because they contain old blood and have a distinctive brown colour. Like the tissue in the lining of the uterus, these growths build up each month but cannot shed during a woman’s menstrual cycle. This can cause painful internal bleeding and the formation of scar tissue.

Most women do not even know they have endometriosis because they experience no symptoms, but for many women, the condition causes extremely painful periods and other pain symptoms. Endometriosis may be associated with chronic pelvic pain and the inability to get pregnant.

Symptoms of endometriosis include:

  • painful periods
  • painful sex
  • pain in the lower abdomen and/or lower back
  • painful bowel movements
  • fatigue
  • heavy or irregular bleeding
  • nausea/dizziness
  • diarrhea/constipation

Approximately 30 to 40 percent of women with endometriosis have trouble getting pregnant.

Impact | Symptoms | Causes

The Impact of Endometriosis

Endometriosis is a chronic illness, which means that once it starts, it usually won't stop on its own. When a woman reaches menopause, the endometriosis usually goes away, though this is not always the case. Even having a total abdominal hysterectomy with both ovaries removed does not always cure endometriosis.

Unlike the normal endometrium, which leaves the body during a woman's period, endometrial growths have no way of leaving the body. This may result in internal bleeding, inflammation of the surrounding areas and the formation of scar tissue.

In some cases, endometriosis might not ever spread or grow, while in other cases, endometriosis may spread throughout the entire pelvic region and beyond.

Endometriosis can affect a woman's ability to get pregnant. Most women experience pain, as well as other symptoms. Generally, women can function on a daily basis but the pain can be so severe that a woman needs to miss work or school. Women do not die from endometriosis. However, there have been some rare, reported cases where women are incapacitated from the pain.

Endometrial growths are not cancerous. However, according to a survey done by the Endometriosis Association, women with endometriosis have a slightly increased risk of developing certain cancers, including melanoma, non-Hodgkins lymphoma, breast cancer and ovarian cancer.


Although we cannot be sure how many women have endometriosis without symptoms, some women who are known to have endometriosis experience no symptoms at all. For other women with the disease, symptoms range from mild to debilitating. Common symptoms include:

Painful Periods (Dysmenorrhea)
Dysmenorrhea is the term used to describe severe pain and cramps right before and during a woman’s period. Pain can also occur at other times throughout the menstrual cycle. Women with endometriosis usually describe their pain as a sharp, knife-like or twisting pain in the pelvis. Approximately 96 percent of women with known endometriosis experience some pain.

Painful Intercourse (Dyspareunia)
Approximately 60 percent of women with endometriosis experience persistent or recurrent pain just before, during and/or after sexual intercourse. Penetration can produce pain in a tender nodule or implant.

Around 80 percent of women with endometriosis feel tired, exhausted or sluggish much of the time.

Heavy or Irregular Bleeding
Endometriosis can cause more frequent, irregular, prolonged and/or heavy periods.

Between 30 and 40 percent of women with endometriosis have problems getting pregnant. Infertility is more common as the disease progresses. Infertility may be the result of the endometriosis interfering with the ovaries and the fallopian tubes.

Bowel Problems
Endometriosis can lead to painful bowel movements, diarrhea, constipation, nausea and other intestinal upsets.


No one knows for sure what causes endometriosis, or why some women develop endometriosis while others do not. There are, however, several theories.

Theory 1 – Retrograde Bleeding

This theory suggests that there is a backward flow of menstrual discharge – and that during a woman's period, the blood flows back through the fallopian tubes into the pelvis. Small pieces of the endometrium can then latch on to the inner lining of the abdomen (the peritoneum) and grow. Approximately 80 to 90 percent of all women have retrograde bleeding but only 10 to 20 percent of them develop endometriosis, so this theory cannot explain the whole story.

Theory 2 – Immune System

Because most women experience retrograde bleeding, some physicians believe that endometriosis occurs only in women who also have an immune problem. Some women's immune systems may not be able to protect against the growth of endometrial tissue within the abdominal cavity.

Theory 3 – Environment

Based on animal studies, some researchers have linked endometriosis to environmental toxins, such as dioxin and PCBs. The Endometriosis Association found that 79 percent of a group of monkeys that had been exposed to dioxin 10 years earlier had developed endometriosis. Researchers found that the more dioxin the monkeys had been exposed to, the more severe their endometriosis. Subsequent research has supported these findings.

Dioxin is a by-product of industrial processes, such as chemical and plastic manufacturing and municipal waste incineration. It can also be found in PVC and vinyl products; soft, flexible plastic products; animal fat; some pesticides; cigarette smoke; and exhaust from gasoline and diesel engines. It is estimated that 90 percent of our exposure to dioxins is through the foods we eat that contain animal fat. (Eating low-fat meat and dairy products and consuming organic products are ways to reduce your exposure.)

Theory 4 – Genetics

We know that in some families endometriosis is more common. A woman has a 15 percent higher chance of developing endometriosis if her mother also has it.

Theory 5 – Blood System or Lymph Vessel Spread

There is some evidence that endometrial tissue can spread from the uterus to other parts of the body, through the blood system or lymph vessels, but why the endometriosis takes root is not known.


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  • A publication of:
  • Women's College Hospital