Endometriosis is a disorder in which tissue resembling the inner lining of the uterus (endometrium) is found outside of the uterus.
Endometriosis is most commonly found on the lining of the pelvic cavity, the ovaries, uterus, on the rectum, the colon and the bladder. It can also be found on the small intestine, liver, spleen, lymph nodes, and in rare cases, elsewhere. If the endometriosis involves an ovary, a blood-filled cyst may develop. This is called an endometrioma, or you may hear it referred to as a chocolate cyst. It’s called a chocolate cyst because the old blood form is dark and appears to be similar to chocolate. These can vary in size from a pea to larger than a grapefruit.
Understanding Your Body
Located in the center of the pelvis, the uterus (womb) is a pear shaped structure. Inside the uterus there is a muscular wall that is covered by a tissue lining known as the endometrium. The endometrium is predominantly made up of mucus secreting glands and blood vessels.
During a woman’s reproductive years, she produces eggs, about once a month while menstruating. The ovaries also produce the hormones estrogen and progesterone. Both of these hormones signal the endometrium to build up in preparation for a fertilized egg to implant. If the egg is fertilized during its journey along the fallopian tube to the uterus, it implants into the thickened endometrium where it can receive nourishment through the blood vessels. If the egg is not fertilized, it passes out of the body, along with part of the endometrium. That is a menstrual period. And that is how the endometrium normally functions.
Who Gets Endometriosis?
Inherited traits and the immune system are important in determining which women actually develop endometriosis. There have been careful genetic studies done that indicate that daughters, sisters or mothers of patients with endometriosis are more likely to have the disease than other women.
Possible Causes of Endometrium
The cause of endometriosis is not known for certain. Several theories have been developed over the last 80 years. However, no single theory described below provides an adequate explanation for the variation and range of locations of endometriosis.
- Retrograde Menstruation
During normal ovulation (the release of an egg from the ovary), the lining of the uterus thickens to prepare for the implantation of a fertilized egg. If implantation does not occur, the lining tissue peels away from the uterus and is expelled in the menstrual flow. In some cases, pieces of the endometrium stray away from the uterus and find their way up, through the Fallopian tubes and into the pelvic cavity (retrograde menstruation). These stray cells implant, where they may continue to act like the uterine lining. They can respond to hormonal cues to grow, thicken and bleed. The endometrial implants that are in close proximity to each other, may adhere together (known as adhesions) and may produce pain or other symptoms. Women who do not menstruate, and those who have had their Fallopian tubes ligated (tied off), appear to have a lower incidence of endometriosis.
In the very early development stages of the fetus, there are only a few cells present which have the potential to change into a number of different types of cells. It is possible that endometriosis may be caused by cells outside of the uterus that, for some reasons unknown, change their function to act like cells in the endometrium.
- Vascular or Lymphatic Spread
It is possible that the endometrium (lining of the uterus) is transported through the blood stream or lymph system to finally deposit and implant in sites remote from the abdomen and pelvis.
- Immune System Abnormalities
Yet another possible cause now under study is a breakdown of the immune system, which normally destroys leftover or misplaced endometriosis cells.