Endometriosis is a disease in which tissue similar to the lining of the uterus grows in other places in the body. It is one of the most common gynecological diseases, and its primary symptoms include pain and infertility.
NICHD conducts and supports research to improve understanding of the mechanisms, diagnosis, and treatments of endometriosis.
Endometriosis is a disease in which tissue similar to the lining of the uterus grows in other places in the body.
The word endometriosis comes from the word “endometrium”—endo means “inside,” and metrium means “uterus,” where a mother carries her baby. Healthcare providers call the tissue that lines the inside of the uterus the endometrium.
Researchers aren’t exactly sure what causes endometriosis, but some theories include the following:
- Retrograde menstruation. This theory proposes that endometriosis cells flow backward through the fallopian tubes and into the pelvis during menstruation.
- Coelomic metaplasia. This theory refers to a change in the characteristics of the cells that line the organs in the pelvis.
These theories don’t explain every instance of endometriosis, like endometriosis that occurs in organs such as the lungs (possibly due to spreading through the blood system or lymphatics) or the rare cases of endometriosis in men.
Healthcare providers may use the terms “implants,” “nodules,” or “lesions” to describe areas or patches of endometriosis. Most endometriosis patches are found in the pelvic cavity:
- On the ovaries
- On the fallopian tubes, which carry egg cells from the ovaries to the uterus
- Behind the uterus
- On the tissues that hold the uterus in place
- On the bowels or bladder
In rare cases, endometriosis may grow outside the pelvic cavity, such as on the lungs or in other parts of the body.1
Researchers’ understanding of endometriosis is changing with new scientific evidence. For example, researchers used to think that pain from endometriosis was related to the size of the patches growing outside the uterus. But evidence shows this is not the case. In fact, the size and location of the lesions are not related to the severity or to the location of the pain.2,3 Studies also indicate that pain is not associated with a woman’s ability to get pregnant.4,5
What are the risk factors for endometriosis?
Research shows that certain factors may increase or decrease a woman’s risk for endometriosis.
What are the symptoms of endometriosis?
The most common symptoms of endometriosis are pain and infertility.1
Other common symptoms of endometriosis include:1
- Painful or even debilitating menstrual cramps, which may get worse over time
- Pain during or after sex
- Pain in the intestine or lower abdomen
- Painful bowel movements or painful urination during menstrual periods
- Heavy menstrual periods
- Premenstrual spotting or bleeding between periods2
- Problems getting pregnant3
For some women, the pain associated with endometriosis gets milder after menopause. However, hormone therapy, such as estrogen or birth control pills given to reduce menopausal symptoms, may cause the pain and other symptoms to continue.
Researchers know that pain is a primary symptom of endometriosis, but they do not know exactly what causes the pain.
The severity of the pain does not correspond with the number, location, or extent of endometriosis lesions. Some women with only a few small lesions experience severe pain; other women may have very large patches of endometriosis but experience little pain.1,6
- Patches of endometriosis respond to hormones in a similar way as the lining of the uterus. These tissues may bleed or have inflammation every month, like a regular menstrual period. However, the blood and tissue shed from endometriosis patches stay in the body and are irritants, which can cause pain.
- In some cases, inflammation and chemicals produced by the endometriosis areas can cause the pelvic organs to stick together, causing scar tissue. This makes the uterus, ovaries, fallopian tubes, bladder, and rectum appear as one large organ.
- Hormones and chemicals released by endometriosis tissue may irritate nearby tissue and cause it to release other chemicals that cause pain.
- Over time, some endometriosis areas may form nodules or bumps on the surface of pelvic organs or become cysts (fluid-filled sacs) on the ovaries.
- Some endometriosis lesions have nerves in them, tying the patches directly into the central nervous system. These nerves may be more sensitive to pain-causing chemicals released in the lesions and surrounding areas. Over time, they may be more easily activated by the chemicals than normal nerve cells are.
- Patches of endometriosis might also press against nearby nerve cells to cause pain.
- Some women report less endometriosis pain after pregnancy, but the reason for this is unclear. Researchers are trying to determine whether the pain reduction results from the hormones the body releases during pregnancy or from changes in the cervix, uterus, or endometrium that occur during pregnancy and delivery.
Endometriosis pain can be severe, interfering with day-to-day activities. Understanding how endometriosis is related to pain is a very active area of research because it could allow for more effective treatments for this type of pain.
How do healthcare providers diagnose endometriosis?
Surgery is currently the only way to confirm a diagnosis of endometriosis.
The most common surgery is called laparoscopy.
In this procedure:
- The surgeon uses an instrument to inflate the abdomen slightly with a harmless gas.
- After making a small cut in the abdomen, the surgeon uses a small viewing instrument with a light, called a laparoscope, to look at the reproductive organs, intestines, and other surfaces to see if there is any endometriosis.
- If patches of tissue are present, the surgeon examines them to determine whether they are endometriosis and, if so, at what stage they might be.
- In some cases, the surgeon will also do a biopsy, which involves taking a small tissue sample and studying it under a microscope, to confirm the diagnosis.1
- The most common surgery is a laparoscopy, but sometimes a laparotomy—a surgical procedure involving a larger incision—is used to make a diagnosis.
Healthcare providers may also use imaging methods to produce a “picture” of the inside of the body. Imaging allows them to locate larger endometriosis areas, such as nodules or cysts. The two most common imaging tests are ultrasound, which uses sound waves to make the picture, and magnetic resonance imaging (MRI), which uses magnets and radio waves to make the picture. These types of imaging do not help diagnose small lesions or adhesions.1
Your healthcare provider will perform a laparoscopy only after learning your full medical history and giving you a complete physical and pelvic exam. This information and exam, in addition to the results of an ultrasound or MRI, will help you and your healthcare provider make more informed decisions about treatment.
Researchers are also seeking less invasive ways to diagnose endometriosis and determine how severe it is. NICHD-funded researchers in the National Centers for Translational Research in Reproduction and Infertility created a “diagnostic classifier” for endometriosis based on the presence of particular genes. The classifier was 90% to 100% accurate. Once the classifier is validated, a simple biopsy in the doctor’s office may be a nonsurgical way to diagnose endometriosis in most women.2
What are the treatments for endometriosis?
There is currently no cure for endometriosis, but there are treatment options for related pain and infertility.
Healthcare providers consider several factors when determining the best treatment for endometriosis symptoms, including:
- Your age
- How severe your symptoms are
- How severe the disease is
- Whether you want children
Not all treatments work well for all women with endometriosis. Also, endometriosis symptoms may return after the treatment is stopped or, in the case of surgery, as more time passes after the procedure.