Endometriosis (en-doe-me-tree-O-sis) is an often painful disorder in which tissue that normally lines the inside of your uterus — the endometrium — grows outside your uterus. Endometriosis most commonly involves your ovaries, fallopian tubes and the tissue lining your pelvis. Rarely, endometrial tissue may spread beyond pelvic organs.
With endometriosis, displaced endometrial tissue continues to act as it normally would — it thickens, breaks down and bleeds with each menstrual cycle. Because this displaced tissue has no way to exit your body, it becomes trapped. When endometriosis involves the ovaries, cysts called endometriomas may form. Surrounding tissue can become irritated, eventually developing scar tissue and adhesions — abnormal bands of fibrous tissue that can cause pelvic tissues and organs to stick to each other.
Endometriosis can cause pain — sometimes severe — especially during your period. Fertility problems also may develop. Fortunately, effective treatments are available.
The primary symptom of endometriosis is pelvic pain, often associated with your menstrual period. Although many women experience cramping during their menstrual period, women with endometriosis typically describe menstrual pain that's far worse than usual. They also tend to report that the pain increases over time.
Common signs and symptoms of endometriosis may include:
- Painful periods (dysmenorrhea). Pelvic pain and cramping may begin before your period and extend several days into your period. You may also have lower back and abdominal pain.
- Pain with intercourse. Pain during or after sex is common with endometriosis.
- Pain with bowel movements or urination. You're most likely to experience these symptoms during your period.
- Excessive bleeding. You may experience occasional heavy periods (menorrhagia) or bleeding between periods (menometrorrhagia).
- Infertility. Endometriosis is first diagnosed in some women who are seeking treatment for infertility.
- Other symptoms. You may also experience fatigue, diarrhea, constipation, bloating or nausea, especially during menstrual periods.
The severity of your pain isn't necessarily a reliable indicator of the extent of the condition. Some women with mild endometriosis have intense pain, while others with advanced endometriosis may have little pain or even no pain at all.
Endometriosis is sometimes mistaken for other conditions that can cause pelvic pain, such as pelvic inflammatory disease (PID) or ovarian cysts. It may be confused with irritable bowel syndrome (IBS), a condition that causes bouts of diarrhea, constipation and abdominal cramping. IBS can accompany endometriosis, which can complicate the diagnosis.
When to see a doctor
See your doctor if you have signs and symptoms that may indicate endometriosis.
Endometriosis can be a challenging condition to manage. An early diagnosis, a multidisciplinary medical team and an understanding of your diagnosis may result in better management of your symptoms.
Although the exact cause of endometriosis is not certain, possible explanations include:
- Retrograde menstruation. In retrograde menstruation, menstrual blood containing endometrial cells flows back through the fallopian tubes and into the pelvic cavity instead of out of the body. These displaced endometrial cells stick to the pelvic walls and surfaces of pelvic organs, where they grow and continue to thicken and bleed over the course of each menstrual cycle.
- Transformation of peritoneal cells. In what's known as the "induction theory," experts propose that hormones or immune factors promote transformation of peritoneal cells — cells that line the inner side of your abdomen — into endometrial cells.
- Embryonic cell transformation. Hormones such as estrogen may transform embryonic cells — cells in the earliest stages of development — into endometrial cell implants during puberty.
- Surgical scar implantation. After a surgery, such as a hysterectomy or C-section, endometrial cells may attach to a surgical incision.
- Endometrial cells transport. The blood vessels or tissue fluid (lymphatic) system may transport endometrial cells to other parts of the body.
- Immune system disorder. It's possible that a problem with the immune system may make the body unable to recognize and destroy endometrial tissue that's growing outside the uterus.
In preparation for ovulation, the lining of the uterus, or endometrium, thickens. If fertilization does not occur, the uterus sheds its lining through the vagina. This is known as menstruation.
In endometriosis, the endometrium grows outside of the uterus. One cause of this growth may be retrograde menstruation.
During retrograde menstruation, menstrual fluid flows backward into the fallopian tubes instead of leaving the body through the vagina. Because the fallopian tubes are open-ended, menstrual backflow can spill into the pelvic cavity.
Backflow of menstrual fluid may promote the transfer of clumped endometrial cells to other tissues in the pelvis. Or menstrual fluid in the pelvic cavity could transform parts of those tissues into endometrial cells.
In either process, clumps of endometrium may start to grow on the tissues lining your pelvic cavity, as well as on your fallopian tubes, ovaries and large intestine. This growth continues to act as it normally would during a menstrual cycle. It thickens, breaks down and bleeds each month.
Because there's nowhere for the blood from this displaced tissue to exit your body, it becomes trapped. Trapped blood may lead to cysts, scar tissue and adhesions, abnormal tissue that binds organs together.
Scarring from endometriosis can block your fallopian tubes. Blocked tubes may keep sperm cells from reaching and fertilizing the egg, causing fertility problems. The menstrual fluid could alter some types of cells in the pelvic cavity to change their structure, or clumps of endometrial tissue contained in the menstrual fluid could stick to the tissues it lands on and start to grow. In either case, this may be a factor in causing endometriosis.
Several factors place you at greater risk of developing endometriosis, such as:
- Never giving birth
- Starting your period at an early age
- Going through menopause at an older age
- Short menstrual cycles — for instance, less than 27 days
- Having higher levels of estrogen in your body or a greater lifetime exposure to estrogen your body produces
- Low body mass index
- Alcohol consumption
- One or more relatives (mother, aunt or sister) with endometriosis
- Any medical condition that prevents the normal passage of menstrual flow out of the body
- Uterine abnormalities
Endometriosis usually develops several years after the onset of menstruation (menarche). Signs and symptoms of endometriosis end temporarily with pregnancy and end permanently with menopause, unless you're taking estrogen.
The main complication of endometriosis is impaired fertility. Approximately one-third to one-half of women with endometriosis have difficulty getting pregnant.
For pregnancy to occur, an egg must be released from an ovary, travel through the neighboring fallopian tube, become fertilized by a sperm cell and attach itself to the uterine wall to begin development. Endometriosis may obstruct the tube and keep the egg and sperm from uniting. But the condition also seems to affect fertility in less-direct ways, such as damage to the sperm or egg.
Even so, many women with mild to moderate endometriosis can still conceive and carry a pregnancy to term. Doctors sometimes advise women with endometriosis not to delay having children because the condition may worsen with time.
Ovarian cancer does occur at higher than expected rates in women with endometriosis. But the overall lifetime risk of ovarian cancer is low to begin with. Some studies suggest that endometriosis increases that risk, but it's still relatively low. Although rare, another type of cancer — endometriosis-associated adenocarcinoma — can develop later in life in women who have had endometriosis.