Endometriosis is the abnormal growth of cells (endometrial cells) similar to those that form the inside or lining the tissue of the uterus, but in a location outside of the uterus. Endometrial cells are cells that are shed each month during menstruation. The cells of endometriosis attach themselves to tissue outside the uterus and are called endometriosis implants. These implants are most commonly found on the ovaries, the Fallopian tubes, outer surfaces of the uterus or intestines, and on the surface lining of the pelvic cavity. They can also be found in the vagina, cervix, and bladder, although less commonly than other locations in the pelvis. Rarely, endometriosis implants can occur outside the pelvis, on the liver, in old surgery scars, and even in or around the lung or brain. Endometrial implants, while they can cause problems, are benign (not cancerous).
Endometriosis affects women in their reproductive years. The exact prevalence of endometriosis is not known, since many women may have the condition and have no symptoms. Endometriosis is estimated to affect over one million women (estimates range from 3% to 18% of women) in the United States. It is one of the leading causes of pelvic pain and reasons forlaparoscopic surgery and hysterectomy in this country. Estimates suggest that between 20% to 50% of women being treated for infertility have endometriosis, and up to 80% of women with chronic pelvic pain may be affected.
While most cases of endometriosis are diagnosed in women aged around 25 to 35 years, endometriosis has been reported in girls as young as 11 years of age. Endometriosis is rare in postmenopausal women. Endometriosis is more commonly found in white women as compared with African American and Asian women. Studies further suggest that endometriosis is most common in taller, thin women with a low body mass index (BMI). Delaying pregnancy until an older age is also believed to increase the risk of developing endometriosis. It also is likely that there are genetic factors that predispose a woman to developing endometriosis, since having a first-degree relative with the condition increases the chance that a woman will develop the condition.