"Ask Dr. Cook" is a series of questions and answers regarding endometriosis. The current subject and answer can be found on Current Ask Dr. Cook web page. The questions may represent a summary of questions I have been asked by several different patients. I hope you find this information helpful. If you have a question you would like answered, please Submit A Question.

What Causes Endometriosis?

Question:
Dr. Cook what is endometriosis and what causes it?

Answer:
Endometriosis is defined as the presence of endometrial tissue outside of the uterus. The uterus is where the baby grows during pregnancy and when it is time to deliver, it pushes the baby out. Most of the uterus is made up of muscle, but it is lined on the inside by a thin layer of glands called the endometrium. This thin layer of glands provides the nutritional support to the developing fetus prior to the development of the placenta (after-birth). The endometrial lining responds to the estrogen during the first two weeks of the menstrual cycle, growing in thickness. You can think of the estrogen as fertilizer for the endometrial lining. After ovulation, during the second half of the cycle, the other female hormone, progesterone, helps to stabilized and mature the endometrial lining. If the woman is not pregnant, both the estrogen and progesterone level drop at the end of the cycle, the endometrial lining sloughs off and her period starts the next day. The menses are made up of the endometrial lining, blood and clots. Most of the menses comes out below, but some flows back up through the fallopian tubes and inside the body. Endometriosis is formed when some of this tissue implants and starts to grow. We don't completely understand why some women develop endometriosis and others do not. It is probably related to both the amount of tissue that a woman's body has to get rid of each month and an inability of her body to recognize or get rid of the endometrial tissue inside of the body cavity. The research to date points to a selective decrease in the immune system. Several studies as well as our own personal experience has shown a decrease in the natural killer cell function (a type of white blood cell).

Retrograde menstruation (backward flow) with implantation of endometrial tissue, as discussed in the previous paragraph, is the cause of endometriosis in the vast majority of cases. Endometrial tissue can spread or form via other less common mechanisms. Extra pelvic endometriosis (endometriosis outside of the pelvic cavity) has been reported in virtually every organ of the body. Most of these rare endometrial implants formed as a result of spread of endometrial tissue through the blood stream (hematogenous spread). Endometriosis has also been reported in the lymph nodes (e.g. obturator lymph nodes). Thus lymphatic spread can cause endometriosis. Endometrial tissue can spread during surgery. The most common example of surgical spread is endometriosis which is found in the abdominal wall following a C-Section. Endometriosis has also been reported in the belly button. This usually presents with bleeding from the navel with menses. Finally, endometriosis can form as a result of what is called coelomic metaplasia. Basically coelomic cells are those formed as a fetus and metaplasia means one cell type turns into another cell type. In other words some of the primitive cells turn into endometriosis in adult life. This probably accounts for the case of endometriosis reported in men. All of the men were on estrogen therapy, I believe for prostatic cancer, which probably stimulated the transformation of the coelomic cells into endometriosis. (Ladies please do NOT slip your significant other a few birth control pills if he is not understanding of your pain)

In conclusion, endometriosis is the presence of endometrial tissue outside of the uterus. Back flow of menstrual tissue through the fallopian tubes with implantation of endometrial tissue is probably the cause of endometriosis in the vast majority of cases.

Updated September 24, 2006