Conditions InDepth: Endometriosis

Endometriosis is a problem with the lining of the uterus (womb). Normally, when you have your menstrual period every month, the lining (endometrial tissue) of the uterus will come out in the menstrual flow.

Endometrial tissue is normally found only inside of the uterus. However, endometriosis refers to the presence of the endometrial tissue outside of the uterus. 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 rectum, bladder, 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.

Endometrial Lesions

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This misplaced endometrial tissue responds to the monthly menstrual hormones. It swells, breaks down, and bleeds. Whereas during the normal menstrual flow the blood exits through the vagina, there is no exit when this tissue is in other locations outside of the uterus. When the blood is trapped inside the body it can irritate surrounding tissue and cause pain and scarring. The pain is increased during the menstrual cycle.

In the United States, 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 25-40.

The exact cause of endometriosis is unknown. Some possible considerations include:

  • Menstrual blood and endometrial tissue flows backward through the fallopian tubes instead of forward through the vagina and out of the body.
  • The immune system does not recognize that there is foreign tissue in the body and allows the tissue to implant and develop in unusual places in the body. This causes endometriosis.
  • The lymph (glands) and/or blood systems carry endometrial cells from the uterus to other areas of the body.
  • Genetic and environmental susceptibility.

What are the risk factors for endometriosis?
What are the symptoms of endometriosis?
How is endometriosis diagnosed?
What are the treatments for endometriosis?
Are there screening tests for endometriosis?
How can I reduce my risk of endometriosis?
What questions should I ask my healthcare provider?
What is it like to live with endometriosis?
Where can I get more information about endometriosis?


American Academy of Family Physicians website. Available at: . Accessed March 2, 2006.

The Endometriosis Association website. Available at: . Accessed March 1, 2006.

Endometriosis Research Center website. Available at: . Accessed March 1, 2006.

Griffith’s 5-Minute Clinical Consult . Lippincott Williams and Wilkins; 1999.

Kistner’s Gynecology and Women’s Health . 7th ed. Mosby-Year Book; 1999.

National Institute of Child Health and Human Development website. Available at: . Accessed March 1, 2006.

National Library of Medicine website. Available at: . Accessed March 2, 2006.

Rakel RE, Bope ET. Conn's Current Therapy 2001 . 53rd ed. Philadelphia, PA: W.B. Saunders Company; 2001.

Last reviewed February 2007 by Jeff Andrews, MD, FRCSC, FACOG

Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.

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