The endometrium is the tissue that lines the inside of the uterus (the womb). It is the tissue that is shed each month when women menstruate. Each month it builds up rapidly in case of pregnancy, and each month the excess endometrial tissue is sloughed off during menstruation if pregnancy does not occur.

In endometriosis, endometrial cells are found outside the uterus, usually in other parts of the abdomen. These cells respond to female hormones in the same way as the lining of the uterus does. Each month, tissue builds up, breaks down, and sheds. Unlike the cells inside the uterus, the blood and tissue that are shed in the abdomen have no way of leaving the body. They stick to other tissue and sometimes start to divide and multiply. They may grow into other tissue, or form strands that bind organs together. They may create scar tissue, which can be painful. Sometimes the endometrial cells create cysts that can rupture and bleed.

The process sounds a bit like cancer, but endometriosis isn't cancer. However, it may very slightly increase the risk of getting certain cancers. Endometriosis isn't a fatal disease, but can be widespread. About 1 in 10 actively menstruating women between the ages of 25 and 44 has endometriosis. About one third to one half of infertile women have the disease.

Various theories have tried to explain endometriosis. Most involve the idea of retrograde flow. During menstruation, the endometrium sheds its top layers. These layers normally leave the body. The tissue and blood is forced out by muscle contractions. Sometimes, however, it flows backwards, going up the fallopian tubes towards the ovaries. Endometrial cells could reach both the ovaries and the pelvic cavity in this way.

Retrograde flow doesn't explain everything though, because it's often seen in women without endometriosis. For endometriosis to develop, something else such as an immune disorder is usually needed. There are measurable differences in the immune systems of women with endometriosis, but we don't know yet what the significance is.

Endometriosis may have a genetic component. The daughters and sisters of women with endometriosis are at a slightly higher risk of getting the disease.

Another theory of endometriosis suggests that it spreads through the blood or lymphatic vessels. There is also the possibility that normal tissue inside the abdominal cavity may change and become endometriosis.

Symptoms of endometriosis include:

• pelvic pain
• pain during sex
• changes in menstruation
• painful urination or bowel movements during periods
• infertility.

Many of these symptoms can also be associated with other health conditions. The severity of symptoms is not necessarily related to the amount of endometrial tissue found outside the uterus. Some women with endometriosis throughout the pelvis feel nothing at all, while others with less tissue found outside the uterus experience a great deal of pain.

Menstrual cramping that worsens after a few years of less painful periods may be a sign of endometriosis.

Cysts and scar tissue can form around the vagina in the abdomen, which can make sexual intercourse painful. Pain during sex is a possible indicator of endometriosis, but it's a symptom of other conditions too. Endometrial tissue often ends up in one or both ovaries of women with endometriosis. There it can form cysts called endometriomas.

A doctor looking for endometriosis will begin by taking a medical history and conducting a pelvic exam. Your doctor will ask about symptoms associated with endometriosis. During the pelvic exam, he or she will check internally for lumps and bumps. This may be followed by an ultrasound of the pelvis to look for cysts on the ovary. Often, the ultrasound may fail to show anything.

If the history and pelvic exam suggest endometriosis, the next step will involve a procedure called laparoscopy. With this procedure, a tiny cut is made near the navel and a thin tube inserted. This tube (the laparoscope) is an illuminated microscope that enables the doctor to clearly see the endometriosis on the outer surfaces of the pelvic organs. The doctor may take a tissue sample during a laparoscopy and a pathologist later examines the tissue sample to confirm if endometriosis was found. At the time of the surgery, the doctor can usually treat the endometriosis with either laser or burning. This will allow patients to have their diagnosis and treatment during the same procedure.

Endometriosis may be treated with medication, laparoscopic surgery, or traditional surgery. The choice of treatment depends on the individual, and is affected by a number of factors, including the woman's age, the severity of her symptoms, and her plans for pregnancy.

Nonsteroidal anti-inflammatory drugs (NSAIDs), including naproxen* and ibuprofen, can be relieve pain. However, they do not treat the underlying cause of the condition. The contraceptive pill is also used in the treatment of endometriosis. Instead of taking the contraceptive for three weeks followed by one week off, you should take it every day. For most women, this eventually causes menstrual bleeding to stop. Medroxyprogesterone may also be used alone to treat endometriosis. Usually, it is given as an injection. Endometriosis can also be treated with medications that create a hormonal state that mimics menopause. These medications, such as danazol, can have masculinizing effects such as deepening of the voice and growth of facial hair.

Laparoscopy and minor surgery can be used to remove endometrial tissue from places where it should not occur, such as the pelvis. During laparoscopy, the doctor will use electricity or a laser to burn off endometrial tissue. Laparoscopy is a less invasive procedure than traditional surgery, and can be done on an outpatient basis (without the person being admitted to hospital). Larger and more embedded growths may require traditional surgery.

Women who do not wish to later become pregnant may opt for a total hysterectomy (removal of the uterus, ovaries, and fallopian tubes). Combined with medication, this procedure eliminates the body's production of female hormones thereby relieving the symptoms of endometriosis. However, there is no guarantee of pain relief. Loss of both ovaries results in estrogen deficiency. Women who undergo this procedure will be offered hormone replacement therapy. Before starting hormone replacement therapy, discuss the risks and benefits of this treatment with your doctor.

*All medications have both common (generic) and brand names. The brand name is what a specific manufacturer calls the product (e.g., Tylenol^®). The common name is the medical name for the medication (e.g., acetaminophen). A medication may have many brand names, but only one common name. This article lists medications by their common names. For more information on brand names, speak with your doctor or pharmacist.