Endometriosis

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Overview, Causes, & Risk Factors

The cause of endometriosis is unknown. However, a number of theories have been proposed. The retrograde-menstruation theory proposes that endometrial cells (loosened during menstruation) may "back up" through the fallopian tubes into the pelvis, where they implant and grow in the pelvic and/or abdominal cavities.

The immune-system theory suggests that a deficiency in the immune system allows menstrual tissue to implant and grow in areas other than the uterine lining. Another theory suggests that the cells lining the abdominal cavity may spontaneously develop endometriosis. A genetic theory proposes that certain families may exhibit predisposing factors that lead to endometriosis.

Once the endometrial cells implant in tissue outside of the uterus, they may become a problem. Each month the ovaries produce hormones that stimulate the cells of the uterine lining to multiply and prepare for a fertilized egg (swell and thicken).

The endometrial cells outside of the uterus also respond to this signal, but they lack the ability to then separate themselves from the surrounding tissue and slough off during the next menstrual period. They sometimes bleed a little bit, but they heal and are stimulated again during the next cycle.

This ongoing process can cause scarring and adhesions in the tubes and ovaries, and around the tubal fimbriae (fingerlike projections at the end of the fallopian tubes). These adhesions can make transfer of an ovum from the ovary to the fallopian tube difficult or impossible. They can also stop passage of a fertilized egg down the fallopian tube to the uterus.

Once in a while the growing cells will penetrate the tough covering of the ovary and begin to multiply. These cells can collect large amounts of blood and form what is called, appropriately, an ovarian blood cyst (endometrioma).

Ovarian blood cysts have been known to grow to the size of a hen's egg or even an orange, and are usually painful. Over time the collected blood darkens and, for this reason, the cysts are frequently called "chocolate cysts".

Endometriosis is a common problem among women, and it occurs in an estimated 10% of them during their reproductive years. The prevalence may be as high as 25% to 35% among infertile women. Although endometriosis is typically diagnosed between the ages of 25 and 35, the problem probably begins about the time that regular menstruation begins.

A woman who has a mother or sister with endometriosis has a risk of developing endometriosis that is 6 times greater than that of the general population. Other possible risk factors include early onset of menstrual periods, regular menstrual cycles, and periods lasting 7 or more days.