Endometriosis is a disease in which patches of
endometrial tissue, which normally is found only
in the uterine lining (endometrium), grow outside
the uterus.
Usually, endometriosis is confined to the lining of the abdominal cavity or the surface of abdominal organs. The misplaced endometrial tissue (endometrial implant) commonly adheres to the ovaries and the ligaments that support the uterus.
Less commonly, it adheres to the outer surface of the small and large intestines, the ureters (tubes leading from the kidneys to the bladder), the bladder, the vagina, surgical scars in the abdomen, or the lining of the chest cavity. Rarely, endometrial tissue is found in the lungs.
Because the misplaced endometrial tissue responds to the same hormones that the uterus responds to, it may bleed during the menstrual period, often causing cramps, pain, irritation, and the formation of scar tissue.
As the disease progresses, adhesions (fibrous bands that connect normally unconnected structures) may form. The misplaced endometrial tissue and adhesions can block or interfere with the functioning of organs. Rarely, adhesions block the intestine.
Who Gets Endometriosis - and Why
Endometriosis can run in families and is more common in first-degree relatives (mother, sister, daughter) of women who have the disease than in other women.
Other factors that increase the risk of endometriosis include giving birth for the first time after age 30, being of Caucasian descent, and having an abnormal uterus.
Endometriosis is estimated to occur in about 10 to 15 percent of menstruating women between the ages of 25 and 44; it can also occur in teenagers. Exactly how many women have this disease is unknown because it usually can be diagnosed only by direct viewing, typically during surgery.
As many as 25 to 50 percent of infertile women may have endometriosis, which can physically interfere with conception. Severe endometriosis may cause infertility by blocking the egg's passage from the ovary into the uterus.
Mild endometriosis also may cause infertility, but how it does so is less clear.
Causes and Symptoms
The exact cause of endometriosis hasn't been established. Cells from the lining of the uterus may somehow move to places outside the uterus, where they continue to grow.
This movement could take place if small pieces of the uterine lining, shed during menstruation, flow backward through the fallopian tubes toward the ovaries into the abdominal cavity, rather than with the menstrual flow through the vagina and outside the body.
Endometriosis can cause pain in the lower abdomen and pelvic area; menstrual irregularities, such as spotting before normal periods; and infertility.
Some women with severe endometriosis have no symptoms, whereas some with minimal disease have incapacitating pain. Often, a woman doesn't have menstrual pain from endometriosis until she's had the disease for several years.
Some women have pain during sexual intercourse (dyspareunia) before or during menstruation.Endometrial tissue attached to the large intestine or bladder may cause abdominal swelling, pain during bowel movements, rectal bleeding during menstruation, or lower abdominal pain during urination.
Endometrial tissue attached to an ovary or a nearby structure can form a blood-filled mass (endometrioma). Occasionally, an endometrioma ruptures or leaks, causing sudden, sharp abdominal pain.
From The Merck Manual
