Endometriosis is a disease occurring very frequently in women of reproductive age, its prevalence being higher than breast cancer. It is also the most misdiagnosed disease.
Endometriosis is the abnormal growth of cells (endometrial cells) similar to those that form the inside 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 for laparoscopic 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 25-35 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.
What causes endometriosis?
The cause of endometriosis is unknown. One theory is that the endometrial tissue is deposited in unusual locations by the backing up of menstrual flow into the Fallopian tubes and the pelvic and abdominal cavity during menstruation (termed retrograde menstruation). The cause of retrograde menstruation is not clearly understood. But retrograde menstruation cannot be the sole cause of endometriosis. Many women have retrograde menstruation in varying degrees, yet not all of them develop endometriosis.
Another possibility is that areas lining the pelvic organs possess primitive cells that are able to grow into other forms of tissue, such as endometrial cells. (This process is termed coelomic metaplasia.)
It is also likely that direct transfer of endometrial tissues during surgery may be responsible for the endometriosis implants sometimes seen in surgical scars (for example, episiotomy or Cesarean section scars). Transfer of endometrial cells via the bloodstream or lymphatic system is the most likely explanation for the rare cases of endometriosis that develop in the brain and other organs distant from the pelvis.
Finally, some studies have shown alternations in the immune response in women with endometriosis, which may affect the body’s natural ability to recognize and destroy any misdirected growth of endometrial tissue.