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Endometriosis: Condition Information

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What is endometriosis?

Endometriosis is the term used to describe when the tissue that normally lines the uterus grows outside the uterus.

The word endometriosis comes from the word "endometrium" (pronounced en-doh-MEE-tree-uhm)-endo means "inside" and metrium (pronounced MEE-tree-uhm) means "uterus," where a mother carries her baby. Health care providers call the tissue that lines the inside of the uterus the endometrium.

Health care providers may use the terms "implants," "nodules," or "lesions" to describe areas or patches of endometriosis. Most endometriosis patches are found in the pelvic cavity:

  • On or under the ovaries
  • On the fallopian tubes, which carry egg cells from the ovaries to the uterus
  • Behind the uterus
  • On the tissues that hold the uterus in place
  • On the bowels or bladder

In rare cases, areas of endometriosis can grow on the lungs or in other parts of the body.1

Researchers' understanding of endometriosis is changing as scientific evidence proves and disproves long-held assumptions. For example, researchers used to think that pain from endometriosis was related to the size of the patches growing outside the uterus. But evidence shows that this is not the case. In fact, the size and location of the lesions are not related to the severity of pain or to the location of the pain.2,3


  1. Office on Women's Health, U.S. Department of Health and Human Services. (2009).Endometriosis fact sheet. Retrieved December 26, 2011, from http://www.womenshealth.gov/publications/our-publications/fact-sheet/endometriosis.html [top]
  2. Stratton, P., & Berkley, K. J. (2011). Chronic pelvic pain and endometriosis: Translational evidence of the relationship and implications. Human Reproduction Update, 17(3), 327-346. [top]
  3. American College of Obstetricians and Gynecologists. (2010). Management of endometriosis (Practice Bulletin No. 114). Obstetrics & Gynecology, 116(1), 223-236. [top]

Last Updated Date: 11/30/2012
Last Reviewed Date: 04/22/2013
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