Endometriosis is the most common cause of chronic pelvic pain in women. It occurs in approximately 10% of menstruating women, 38% of infertile women and is found in close to 80% of women who have chronic pain. The pain can sometimes be quite debilitating, interfering with the quality of life.

It is a chronic, relapsing condition with an unknown trigger. There appears to be a slight genetic association as there is 7-10% increased risk in women with an affected first-degree relative and a strong concordance in identical twins. Other risk factors include never pregnant, onset of menarche before age 11, cycles less than 27 days and heavy prolonged menses. Women, who have delivered more children, had a longer period of breast-feeding and exercise more than 4 hours per week are less likely to develop endometriosis. The course is unpredictable for the individual but of those with a known diagnosis, 31% will worsen, 31% will have persistent but unchanged symptoms and 38% will experience improvement over time without treatment. Even those who are treated have a 45% chance of recurrence after 5 years.

Endometriosis is the implantation of endometrial tissue in sites other than the uterus. Endometriotic implants are commonly found in the pelvic cavity growing on the ovaries and tubes, and in the peritoneum behind the uterus, over the bladder, on the sidewall and over the rectum. Less common sites include abdominal incisions, in the bladder and in the wall of the rectum. There are even reported cases of it being found in the lungs.

No one knows how endometrial tissue gets to these sites but there are a few theories. One theory is that of retrograde menstruation. The endometrium, which is normally shed through the cervix and into the birth canal, is thought to also shed back through the fallopian tube and into the pelvis. This tissue then implants and grows in response to estrogen. It is common to find menstrual blood in the pelvis during menstruation if a laparoscopy is performed at the time of menses. The other theory is that the tissue in the pelvis undergoes a transformation called metaplasia changing into endometrial tissue, which then responds to hormonal fluctuation. The last theory involves the metastasis of the endometrial tissue. The tissue travels from the uterus via the blood stream or lymphatic system to the affected sites, implanting and growing in response to estrogen.

The ectopic endometrial tissue grows and changes in response to increased estrogen levels, which also fluctuates through the ovulatory cycle. These are the same changes the endometrium goes through normally to prepare for implantation of the fertilized egg and to shed if implantation does not occur. Thus the pain of endometriosis is typically cyclic, especially in the early stages. The presence of the tissue in the pelvis cause adhesion formation and scarring which also contributes to the pain. Sometimes the tissue can grow on the ovary producing a cyst called an endometrioma.

Not every woman who has endometriosis will experience pain but in those who do the pain can be progressive. Pain with the period, premenstrual pain and infertility are the most common indicators of this condition. In some cases the pain can be managed with analgesics or hormonal therapy but a definitive diagnosis can only be made by surgery. If you are experiencing these symptoms, it is important to seek the care of a gynecologist.

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