Causes of Endometriosis

What is Endometriosis? | Causes of Endometriosis | Symptoms | How is it Diagnosed? | Treatments for Endometriosis

 

Karl von Rokitansky, Austrian physician and pathologist.

Short History of Endometriosis

The term endometriosis is used to describe the presence of endometrial tissue outside of the uterine cavity. The first morphologic description of this condition was made on a skin lesion in 1690 by Daniel Christian Schrön, a German physician. Later, in 1860, Karl von Rokitansky, an Austrian physician and pathologist, presented further descriptions of endometriosis from a pathological point of view.

Despite the long history of endometriosis and the research happening on the condition worldwide, there is no known root cause of endometriosis. This is most likely because endometriosis does not have a single disease pathway, a fact that is reflected by the many different clinical manifestations of the disease, areas of the body it affects, levels of severity, and symptoms experienced by many individuals.

“Despite the long history of endometriosis and the research happening on the condition worldwide, there is no known root cause of endometriosis.”

Common to all proposed theories, is that oestrogen is required for the endometriotic lesions to grow and expand. For this reason,  endometriosis is hardly ever seen in young individuals before they start menstruating or in individuals who have reached menopause.

Below are the main theories regarding the origin of endometriosis proposed by scientists :

Retrograde Menstruation

 Retrograde menstruation is one of the most recognized endometriosis theories. It assumes that the cause of endometriosis is associated with a partial reversal of the menstrual flow through the fallopian tubes. Typically, menstrual flow (containing the endometrial cells) flows out of the uterus, through the cervix and vagina. In the case of retrograde menstruation, some of this flow can move backwards through the fallopian tubes, where it can reach the other tissues of the pelvis and abdomen.

While this might sound strange and unusual, 9 out of 10 individuals who menstruate experience retrograde menstruation. This process can also occur between menstrual bleeding times in the cycle, such as shortly before ovulation, where the uterus generates some suction to draw in sperm for egg fertilization. During this event, endometrial cells can get caught up in the suction as well and exit the uterus through the fallopian tubes to enter the pelvic and abdominal cavities. Some of the endometrial cells that reach the abdominal cavity and manage to implant into the pelvic and abdominal organs will grow to form ectopic endometrial implants.

 

Coelomic Metaplasia Theory of Endometriosis - Cells with a similar embryonic origin as the endometrial cells may be found in other areas of the body and under specific conditions, may be triggered to develop into endometrial tissue; thereby causing the development of endometriotic lesions.

Coelomic Metaplasia

Coelomic metaplasia states that endometriosis develops directly on regions outside the uterus (e.g. ovaries, bladder, and bowels) via cells that have a similar embryonic origin as the endometrial cells within the uterus. Under specific conditions, these cells may be triggered to develop further into endometrial tissue and create the endometriotic lesions seen in endometriosis. This theory is believed to explain how endometriosis can develop in areas distant from the pelvis, such as the diaphragm and lungs.

 

Immunologic and Genetic Theories

Immunologic theories believe that endometriosis develops from changes in the immune system. In this theory, it is thought that antibodies specifically targeting the endometrial cells are formed, which can lead to an immune response and cause inflammation in the affected areas, thereby damaging the surrounding tissues.

However, it is still unclear as to whether this immune system change causes endometriosis or if the immune system change is a response to endometriosis that was already present.

Theories based on genetics have been proposed for endometriosis because it occurs more often in particular families. The risk of individuals with a close relative with endometriosis (e.g. a parent or sibling)also developing the condition is increased by 7-fold. Though this increased risk suggests a genetic predisposition, there is no specific ‘endometriosis gene’ that has been identified.

 

Genetic/Epigenetic Theory

The Genetic/Epigenetic Theory is the most recent theory and suggests that endometriotic lesions can originate from endometrial tissue, bone marrow, or stem cells that have inherited genetic and/or epigenetic defects.

According to the theory, most individuals with uteruses develop microscopic endometriotic lesions. These can either regress spontaneously or progress into bigger lesions depending on additional factors.

This theory is similar to the one used to explain multistep development of some tumours.