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In endometriosis, patches of endometrial tissue—normally occurring only in the lining of the uterus (endometrium)—appear outside the uterus.
Why endometrial tissue appears outside the uterus is unknown.
Endometriosis can impair fertility and cause pain (particularly before and during menstrual periods and during sexual intercourse), but it may cause no symptoms.
Doctors check for endometrial tissue by inserting a thin viewing tube through a small incision near the navel (laparoscopy).
Drugs are used to relieve pain and to slow the growth of the misplaced tissue.
Surgery may be done to remove the endometrial tissue outside the uterus and sometimes the ovaries.
Endometriosis: Misplaced Tissue
Endometriosis is a chronic disorder that may be painful. Exactly how many women have endometriosis is unknown because it can usually be diagnosed only by directly viewing the endometrial tissue (which requires a surgical procedure). About 6 to 10% of all women have endometriosis. The percentage of women who have endometriosis is higher among women who are infertile (25 to 50%) and women who have pelvic pain (75 to 80%). The average age at diagnosis is 27, but endometriosis can develop in adolescents.
Endometriosis sometimes runs in families and is more common among first-degree relatives (mothers, sisters, and children) of women with endometriosis. It is more likely to occur in women who have their first baby after age 30, who have never had a baby, who have short menstrual cycles (less than 27 days), or who have certain structural abnormalities of the uterus.
Endometriosis seems to occur less often in women who have had several pregnancies, who use low-dose oral contraceptives, or who exercise regularly (especially if they started before age 15, exercise more than 4 hours a week, or both).
The cause of endometriosis is unclear, but there are several theories:
Small pieces of the lining of the uterus (endometrium) that are shed during menstruation may flow backward through the fallopian tubes toward the ovaries into the abdominal cavity, rather than flow through the vagina and out of the body with the menstrual period.
Cells from the endometrium (endometrial cells) may be transported through the blood or lymphatic vessels to another location.
Cells located outside the uterus may change into endometrial cells.
Common locations of misplaced endometrial tissue (called implants) include the following:
Less common locations include the fallopian tubes, the outer surface of the small and large intestines, the ureters (tubes leading from the kidneys to the bladder), the bladder, and the vagina. Rarely, endometrial tissue grows on the membranes covering the lungs (pleura), the sac that envelops the heart (pericardium), the vulva, the cervix, or surgical scars in the abdomen.
The misplaced endometrial tissue responds to hormones as normal endometrial tissue does. Thus, it can bleed and cause pain, particularly before and during menstrual periods. The severity of symptoms and the disorder's effects on fertility and on organ function vary greatly from woman to woman.
As the disorder progresses, the misplaced endometrial tissue tends to gradually increase in size. It may also spread to new locations. However, how much tissue is present and how quickly endometriosis progresses vary greatly. The tissue may remain on the surface of structures or may penetrate deeply (invade) and form nodules.
The pain usually varies during the menstrual cycle, worsening before and during menstrual periods. Menstrual irregularities, such as heavy menstrual bleeding and spotting before menstrual periods, may occur. Misplaced endometrial tissue responds to the same hormones—estrogen and progesterone (produced by the ovaries)—as normal endometrial tissue in the uterus. Consequently, the misplaced tissue may bleed during menstruation and often causes cramps and pain.
The severity of endometriosis symptoms does not depend on the amount of misplaced endometrial tissue. Some women with a large amount of tissue have no symptoms. Others, even some with a small amount, have incapacitating pain. In many women, endometriosis does not cause pain until it has been present for several years. For some women, sexual intercourse tends to be painful before or during menstruation.
Symptoms also vary depending on where the endometrial tissue is located. Possible symptoms by location include
Large intestine: Abdominal bloating, pain during bowel movements, or diarrhea, constipation, or rectal bleeding during menstruation
Bladder: Pain above the pubic bone during urination and urine that contains blood
Ovaries: Formation of a blood-filled mass (endometrioma), which sometimes ruptures or leaks, causing sudden, sharp abdominal pain
The misplaced endometrial tissue and its bleeding may irritate nearby tissues. As a result, scar tissue may form, sometimes as bands of fibrous tissue (adhesions) between structures in the abdomen. The misplaced endometrial tissue and adhesions can interfere with the functioning of organs. Rarely, adhesions block the intestine.
Severe endometriosis may cause infertility when the misplaced tissue blocks the egg's passage from the ovary into the uterus. Mild endometriosis may also cause infertility, but how it does so is less clear.
During pregnancy, endometriosis may become inactive (go into remission) temporarily or sometimes permanently. Endometriosis tends to become inactive after menopause because estrogen levels decrease.
A doctor may suspect endometriosis in a woman who has typical symptoms or unexplained infertility. Occasionally, during a pelvic examination, a woman may feel pain or tenderness, or a doctor may feel a mass of tissue behind the uterus or near the ovaries.
If endometriosis is suspected, a doctor examines the abdominal cavity with a thin viewing tube (called a laparoscope) to check for endometrial tissue. The laparoscope is inserted into the abdominal cavity (the space around the abdominal organs) through a small incision most often made just above or below the navel. Carbon dioxide gas is inserted into the abdominal cavity to distend it so that organs can be viewed more easily. The entire abdominal cavity is examined. If a doctor sees abnormal tissue and is not sure that it is endometrial tissue, a biopsy may be done. A sample of the tissue is removed, using instruments inserted through the laparoscope. The sample is then examined using a microscope. Laparoscopy usually requires a general anesthetic, but an overnight stay in the hospital is usually required only if a very large amount of abnormal tissue is removed. Laparoscopy causes mild to moderate abdominal discomfort, but normal activities can usually be resumed in a few days.
Depending on the location of the misplaced tissue, a biopsy may be done when the vagina is inspected during a pelvic examination or when a flexible viewing tube is inserted through the anus to examine the lower part of the large intestine, rectum, and anus (sigmoidoscopy) or bladder (cystoscopy).
Other procedures may be used to determine the extent of endometriosis and follow its course, but their usefulness for diagnosis is limited. These tests include ultrasonography, x-rays taken after a barium enema, computed tomography (CT), and magnetic resonance imaging (MRI).
If a woman is infertile, tests may be done to determine whether the cause is endometriosis or another disorder.
Doctors classify endometriosis as minimal (stage I), mild (stage II), moderate (stage III), or severe (stage IV) based on the amount of misplaced tissue, its location, and its depth (whether it is on the surface of or deep within an organ) and on the presence and number of endometriomas and adhesions. Doctors may use the following to estimate what the chances of becoming pregnant are for a woman with endometriosis:
Usually, nonsteroidal anti-inflammatory drugs ( NSAIDs) are used to relieve pain. They may be all that is needed if symptoms are mild and women do not plan to become pregnant.
Other drugs can be used to suppress the activity of the ovaries and thus slow the growth of the misplaced endometrial tissue and reduce bleeding and pain. These drugs include
However, these drugs may not eliminate endometriosis, and even if they do, endometriosis often recurs after the drugs are stopped unless more radical treatment is used to completely and permanently stop the ovaries from functioning.
Combination oral contraceptives are used primarily in women who do not plan to become pregnant soon. Oral contraceptives may also be used after treatment with danazol or a GnRH agonist to try to slow progression of the disorder and to reduce pain. The oral contraceptives can be taken continuously, especially if pain is worse during menstrual periods. If combination oral contraceptives are not effective, women may be given an aromatase inhibitor in addition to the oral contraceptive. This treatment is sometimes effective.
GnRH agonists turn off the brain's signal to the ovaries to produce estrogen and progesterone. As a result, production of these hormones decreases. Continued use of GnRH agonists for more than 4 to 6 months causes a decrease in bone density and may lead to osteoporosis. To minimize the decrease in bone density, doctors may give women small doses of a progestin or a bisphosphonate (such as alendronate, ibandronate, or risedronate).
Danazol inhibits release of an egg (ovulation). However, it has side effects including weight gain and the development of masculine characteristics (such as increased body hair, loss of hair from the head, reduced breast size, and lowering of the voice). These side effects limit its use.
After treatment with drugs, fertility rates range from 40 to 60%. Drugs do not change fertility rates in women with minimal or mild endometriosis.
Drugs Commonly Used to Treat Endometriosis
For most women with moderate to severe endometriosis, the most effective treatment is removing or destroying misplaced endometrial tissue and endometriomas. Usually, these surgical procedures are done through a laparoscope inserted into the abdomen through a small incision made near the navel. Such treatment may be needed in the following situations:
When adhesions in the lower abdomen or pelvis cause significant symptoms
When misplaced endometrial tissue blocks one or both fallopian tubes
When drugs cannot relieve severe lower abdominal or pelvic pain
When endometriomas are present
When endometriosis causes infertility and the woman wants to be able to become pregnant
Often, misplaced endometrial tissue can be surgically removed, or if it cannot be removed, it can be destroyed during laparoscopy when the diagnosis is made. Sometimes electrocautery (a device that uses an electrical current to produce heat) or a laser is used to destroy or remove endometrial tissue during laparoscopy or abdominal surgery (involving an incision into the abdomen).
Endometriomas are drained and removed whenever possible.
If pain is persistent, the misplaced endometrial tissue may be removed, the nerve pathways that conduct pain sensation from the pelvis to the brain may be interrupted, or both may be done.
During surgery, doctors remove as much misplaced endometrial tissue as possible without damaging the ovaries. Thus, the woman's ability to have children may be preserved. Depending on the extent of the endometriosis, 40 to 70% of women who have surgery may become pregnant. If doctors cannot remove all of the tissue, women may be treated with a GnRH agonist. But whether this drug increases their chances of becoming pregnant is unclear. Some women who have endometriosis can become pregnant by using assisted reproductive techniques, such as in vitro fertilization.
Surgical removal of misplaced endometrial tissue is only a temporary measure. After the tissue is removed, endometriosis recurs in most women unless they take drugs to suppress the ovaries or the ovaries are removed.
Removal of both ovaries and the uterus (oophorectomy plus hysterectomy) is appropriate only when drugs do not relieve abdominal or pelvic pain in women who do not plan to become pregnant. Removal of the ovaries and uterus has the same effects as menopause because it, like menopause, results in decreased estrogen levels. Thus, women under 50 may be given estrogen to reduce the severity of the menopausal symptoms that occur after this surgery. However, to help prevent endometriosis from recurring, doctors usually recommend that women wait 3 to 6 months after surgery before starting estrogen. Most of these women are also given a progestin. The progestin is included to help prevent any remaining misplaced endometrial tissue from growing. A progestin alone can be given to women over 50 to reduce symptoms that persist after the ovaries are removed.
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