Endometrium is the tissue that lines the uterus (the womb). During the menstrual cycle the thickness of the endometrium increases in readiness for the fertilised egg. If pregnancy does not occur the lining is shed as a ‘period’.
Endometriosis is a condition where the cells that are normally found lining the uterus are also found in other areas of the body but usually within the pelvis. Each month this tissue outside of the uterus, under normal hormonal control, is built up and then breaks down and bleeds in the same way as the lining of the uterus. This internal bleeding into the pelvis, unlike a period, has no way of leaving the body. This leads to inflammation, pain and the formation of scar tissue.
Endometrial tissue can also be found in the ovary where it can form cysts, called ‘chocolate’ cysts. Endometrial deposits can also be found less often in more remote sites than the pelvis. Endometriosis can be found in or on the bowel, in or on the bladder, in operation scars and extremely rarely even in the lungs. It is also possible to have endometrial tissue that grows in the muscle layer of the wall of the uterus. This is called adenomyosis. Each month this tissue within the muscle wall bleeds in the same way as the endometrial tissue in the pelvis bleeds. Adenomyosis can also be found in the muscle layer of the perineum – in the pouch of Douglas or cul de sac. It has to be clear that endometriosis is not an infection, is not contagious and is not cancer.