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Endometriosis refers to the presence of the endometrial tissue outside of the uterus. The lining is called the endometrium. Normally, when you have your menstrual period every month, the lining will come out in the menstrual flow through the vagina.
Endometrial tissue is normally found only inside of the uterine cavity. The most common sites include the ovaries, the outside surface of the uterus, the fallopian tubes, ligaments of the pelvis, and the spaces between the rectum, bladder, and uterus. Less commonly, the intestine and appendix may be involved. Rarely, deposits (or implants) of endometrial tissue may be found in the lung, arm, thigh, and skin far away from the reproductive tract.
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This misplaced endometrial tissue responds to the monthly cycles of reproductive hormones. It swells, breaks down, bleeds, and causes an inflammatory reaction. During menstruation, the blood exits through the vagina. With endometriosis, there is no exit because the tissue is in other locations outside of the uterus. The pain is increased during the latter part of the menstrual cycle and the beginning of menses.
In the US, endometriosis affects an estimated 10%-20% of women of reproductive age. Although endometriosis may occur at any age, it is most commonly seen between the ages of 25 and 40.
The exact cause of endometriosis is unknown. Some possible considerations include:
Endometriosis is a major factor in female infertility. In fact, about 30%-45% of all women who are being treated for infertility have evidence of endometriosis.
Endometriosis. EBSCO DynaMed Plus website. Available at:http://www.dynamed.com/resultlist/dmp~AN~T900174/Epilepsy-in-children?q=endometriosis&filter=all. Updated May 25, 2017. Accessed September 12, 2017.
What is endometriosis? Endo-Online website. Available at: http://www.endometriosisassn.org/endo.html. Accessed September 12, 2017.
Last reviewed September 2018 by EBSCO Medical Review Board Beverly Siegal, MD, FACOG Last Updated: 9/17/2014