Causes

In spite of the high prevalence of endometriosis in women all over the world, researchers have been unable to determine its cause. A combination of genetic, biologic, and environmental factors appear to work together to trigger the initial process, to produce implantation, and to trigger subsequent reseeding and spreading of the implants.

Initial Cause and Distribution of Endometriosis

Retrograde Menstruation. One favored explanation for the development of endometriosis implants involves retrograde menstruation. This occurs when, during a woman's period, menstrual tissue flows backward through the fallopian tubes, rather than flowing out through the vagina. Early theorists suggested that in some cases, the redistributed uterine tissue attached and grew in areas outside the uterus, forming endometriosis implants. This theory does not fully explain endometriosis, however. Many women experience some retrograde menstruation, but not all of them develop endometrial cysts. Consequently, other factors must be at work to explain why uterine tissue becomes implanted and grows in areas outside the uterus.

Text Continues Below

---

Lymphatic Transport. It has been suggested that endometriosis first develops when uterine tissue is separated and then is transported to other organs by way of the lymphatic system or the blood stream.

The lymphatic system filters fluid from around cells. It is an important part of the immune system. When people refer to swollen glands in the neck, they are usually referring to swollen lymph nodes. Common areas where lymph nodes can be easily felt, especially if they are enlarged, are: the groin, armpits (axilla), above the clavicle (supraclavicular), in the neck (cervical), and the back of the head just above hairline (occipital).