The aetiology of the disease is still unknown (1).
Many hypotheses have been suggested to explain the basis of endometriosis but none are fully accepted. Probably, a variety of mechanisms operate. The main theories include:
- implantation due to retrograde menstruation -
- the most widely excepted theory for the development of pelvic endometriosis (2)
- endometrial tissue reflux through the fallopian tubes at the time of menstruation to implant and grow on the peritoneal and ovarian surfaces
- reflux menstruation is seen in around 80% of women but not all women develop endometriosis (2)
- metaplasia of coelomic derivatives -
- endometriosis results from metaplastic transformation of peritoneal mesothelium into endometrium due to rising oestrogen levels seen at puberty (2)
- the factors responsible have yet to be identified.
- embolism of endometrial tissue in pelvic veins or lymphatics -
- endometrial tissue has been found in pelvic lymphatics in 20% of patients
- this has been used to explain the rare endometric lesions seen at distant sites e.g. brain, lung (2)
- implantation in sites of injury -
- for example, after Caesarean section or episiotomy
In addition to the above, immunological dysfunction (which interferes with clearing of viable endometrial cells), peritoneal dysfunction and genetic defects are thought to be important as well (1).
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