Endometriosis: What You Need to Know

Endometriosis is a condition in which endometrial tissue —tissue that normally lines the inner wall of the uterus— is present outside of the uterus. Usually, this means present somewhere else in the pelvis. Such tissue is called ectopic endometrial tissue and when there’s a clump of such ectopic endometrial tissue on an ovary, sometime it is called an endometrioma. The symptoms that you can suffer from endometriosis are numerous and they often vary based on the location, or locations, of the ectopic endometrial tissue. Endometrium on the cervix or vagina, for instance, can cause post-coital bleeding (bleeding after intercourse) and dyspareunia, meaning pain during intercourse. Endometrium on the bladder can cause painful urination, while endometrium on the rectum can cause pain when you defecate. Endometrium on the ovaries and in the fallopian tubes can cause fertility problems. There also can be endometrium anywhere else in the abdominopelvic cavity, causing abdominal and pelvic pain, and even spontaneous hemorrhage in the cavity.

Symptoms of endometriosis tend to wax and wane and can worsen during pregnancy. There is a very good reason for this. Just like the endometrium that’s located properly on the inner wall of your uterus, endometrial tissue that’s ectopic responds to hormonal changes. The hormonal environment changes throughout the menstrual cycle and also changes during pregnancy. The hormone estrogen stimulates endometrial growth, while progestin hormones do the opposite. They discourage endometrial growth. Also, when hormone levels drop, as they do toward the end of your menstrual cycle, the thickened endometrial layer that has built up starts shedding. This is what causes the bleeding of your period, but when you have endometriosis, the inside of the uterus is not the only place where endometrium is located and has thickened up. Thus, when it’s time for you to bleed from the normal endometrium in the uterus, it’s also a time when ectopic endometrium will bleed, although, as with the period, bleeding also can occur with irregular timing. In contrast with the endometrium inside your uterus, ectopic endometrium inside your abdomen and pelvis has nowhere to go when it shed. Furthermore, when it thickens it can put pressure on whatever structure it sits. The pressure from endometrial thickening and shedding causes pain and also can interfere with organ function.

As for the pathophysiology of endometriosis, the abnormal process leading to the conditions, doctors and scientists are not completely sure, but there are a handful of hypotheses:

Retrograde menstruation: One hypothesis is that ectopic endometrium comes from retrograde menstruation. Normally, in menstruation, endometrium is shed, including endometrial cells and blood, exits the uterus by way of the cervix and vagina. In retrograde menstruation, these materials move the other way, through one or both fallopian tubes, so they end up in the pelvis. It’s normal to have a tiny bit of retrograde menstruation each month and the body has ways to deal with it, but according to the retrograde menstruation hypothesis, some number of endometrial cells take hold somewhere outside the uterus, initiating endometriosis.

Metaplasia: Another hypothesis is that certain cells in the pelvis transform into endometrial cells, which is an example of a process called metaplasia, the replacement of one type of differentiated cell with another type.

Spread through blood and lymphatics. This hypothesis states that stem cells generate endometrial cells that are spread through blood and lymphatic vessels.

Immune hypothesis. This is an idea that ectopic endometrial tissue develops due to a complex chain of events involving the immune system

The following factors are associated with endometriosis: You are nulliparous, meaning that you have never given birth; early menarche, meaning that your period began when you were very young; late menopause (your period stopped when you were fairly old; short menstrual cycles, such as cycles lasting under 27 days; menorrhagia (heavy menstrual periods that last longer than seven days); unusually high levels of estrogen in the body; low body mass index (being very thin, underweight); endometriosis in a family member, such as your mother, sister, or aunt; medical conditions in which menstrual blood has difficulty exiting through the cervix body; various reproductive tract disorders.

Of the situations listed above, notice that many of them involve having a lot of blood move through your uterus over the long course of time. If you start menstruating at a young age, or continue menstruating until an older age, that’s more blood than usual. If your cycles are short, that’s also more blood than usual, since the time gaps between periods are shorter; you have more periods within a given span of time. The same goes for menorrhagia; if your periods are especially heavy and/or last more days than the average period, that’s also more blood. All of these situations involving a lot of blood dovetail with the retrograde menstruation and the metaplasia hypotheses. Similarly, having a lot of estrogen promotes thickening of endometrial tissue and more shedding and bleeding. Additionally, any situation that makes it difficult for blood to leave through the cervix dovetails with the retrograde menstruation hypothesis, since difficulty passing through the cervix means that more blood will be encouraged to move retrograde, through the fallopian tubes.

Complications of endometriosis include infertility and cancer, but there are ways to treat endometriosis to minimize fertility problems and to reduce the cancer risk. These treatments include medical approaches, such as oral contraceptives, agents that affect gonadotropin-releasing hormone (Gn-RH, a brain hormone that causes the pituitary to release luteinizing hormone and follicle-stimulating hormone, which affect the ovaries), progestin, and aromatase inhibitors (medicines that interfere with the production of estrogen). For cases in which medical treatment is not enough, there are surgical options.

David Warmflash
Dr. David Warmflash is a science communicator and physician with a research background in astrobiology and space medicine. He has completed research fellowships at NASA Johnson Space Center, the University of Pennsylvania, and Brandeis University. Since 2002, he has been collaborating with The Planetary Society on experiments helping us to understand the effects of deep space radiation on life forms, and since 2011 has worked nearly full time in medical writing and science journalism. His focus area includes the emergence of new biotechnologies and their impact on biomedicine, public health, and society.

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