What causes endometriosis?

The cause of endometriosis remains unknown. There are several theories, but none of them has been entirely proven. The most accepted theory is centred on the so-called retrograde menstruation. During menstruation, pieces of endometrium arrive in the abdominal cavity through the Fallopian tubes, adhere to the peritoneal lining and develop into endometriotic lesions. The hormone estrogen is crucial in this process. Subsequently, most of the current treatments for endometriosis attempt to lower estrogen production in a woman’s body in order to relieve her of symptoms.
It has been argued that endometriosis is a genetic disease, since some families show more patients with endometriosis compared to other families. Other suggestions are an immune response triggering inflammation.


How can you reduce the chances of getting endometriosis?

Doctors sometimes get questions from relatives of women with endometriosis on how they can prevent the disease.
Studies investigating whether taking the oral contraceptive pill or regular exercise could prevent endometriosis did not show a clear causal relation and have limitations. Therefore, it is uncertain whether taking the combined oral contraceptive pill or having regular physical exercise will prevent the development of endometriosis. Other interventions have not been studied.
Up to now, there are no know ways to reduce the chance of getting endometriosis.


How can endometriosis be classified?

A staging system has been developed by the American Society of Reproductive Medicine (ASRM) to stage endometriosis and adhesions due to endometriosis. This classification is often used by gynaecologists to document any endometriosis and adhesions that are visualized during surgery. While a higher stage is generally regarded as denoting a more severe form of disease, the staging system neither predicts severity of pain nor complexity of surgery. The classification was originally developed to predict impairment to fertility and for this reason is focused on ovarian disease and adhesions. Patients with the same ‘stage’ of disease may have different disease presentations and types. Furthermore, some forms of severe disease are not included e.g., invasive disease of the bowels, bladder and diaphragm. The four stages of the ASRM staging system for endometriosis are as follows:
Stages 1 & 2 (minimal to mild disease): Superficial peritoneal endometriosis. Possible presence of small deep lesions. No endometrioma. Mild filmy adhesions, if present.
Stages 3 and 4 (moderate to severe disease): The presence of superficial peritoneal endometriosis, deeply invasive endometriosis with moderate to extensive adhesions between the uterus and bowels and/or endometrioma cysts with moderate to extensive adhesions involving the ovaries and tubes.
As a patient, your stage of disease does not indicate your symptoms nor necessarily the optimal treatment to manage those symptoms. However, the subtype(s) of disease that you have may well be informative in deciding upon optimal treatment.

Apart from the classification system 3 subtypes of endometriosis can be discerned according to localization: superficial peritoneal endometriosis, cystic ovarian endometriosis (endometrioma or ‘chocolate cysts’) and deep endometriosis (also referred to as deeply infiltrating endometriosis). The different types of disease may co-occur (i.e., a patient may have more than one type of disease present in her pelvis).
Superficial peritoneal endometriosis: The most common type is superficial peritoneal endometriosis. The lesions involve the peritoneum, which is a thin film that cloaks the inner surfaces of the pelvic cavity. The lesions are flat and shallow and do not invade into the space underlying the peritoneum.
Cystic ovarian endometriosis (ovarian endometrioma): Less commonly women with endometriosis can develop endometrioma in their ovaries. An endometrioma is a cyst in which the wall of the cyst contains areas of endometriosis. The cyst is filled with old blood. Because of the colour, the cysts are also referred to as ‘chocolate cysts’. Most women with endometrioma cysts will also have superficial and/or deep disease present elsewhere in the pelvis.
Deep endometriosis: Lastly, the least common subtype of endometriosis is deep endometriosis. An endometriosis lesion is defined as deep if it has invaded at least 5mm beyond the surface of the peritoneum. Given the peritoneum is very thin, deep lesions always involve tissue underlying the peritoneum (the retroperitoneal space).