What causes endometriosis?

As mentioned, this endometrial lining is the layer that lines the uterine cavity. However, in a certain percentage of women, sections of endometrial tissue are found in a different location in the pelvis or abdomen: the ovaries, uterus, fallopian tubes, intestines, bladder, ligaments - that hold the uterus and in the Douglas pouch (the area between the uterus and the intestines). In less common cases, the tissue can be found in the stomach and diaphragm and even in the pericardium.

It is unclear exactly why the tissue that should normally be found in the uterus arrives outside it. However, despite this tissue being found outside the uterus, it continues to behave as uterine endometrium, that is, it is affected by the same sex hormones - estrogen and progesterone.

During the body's hormonal cycle, which lasts an average of four weeks, these hormones are responsible for the thickening of the lining of the uterus in the first part of the cycle, and in the second half, if there is no pregnancy, they are responsible for the breakdown and bleeding of the lining.

Unlike the uterine lining in the uterus that passes through the cervix and vagina and essentially constitutes the menstrual period, the tissue that lies outside the uterus has nowhere to bleed to except onto the surface of the organs and tissues around it.

This causes irritation, which leads to infection, scar formation (abnormal fibrotic tissue) and sometimes to the creation of adhesions between organs.

As the disease progresses, the areas with abnormal uterine lining grow and may ultimately create cysts. Usually, the cysts are small (less than 2 cm in diameter), but they can reach a size of 10 cm and more. The cysts in the ovaries are called "chocolate cysts" or endometriomas.