We are getting to the very important observation that endometriosis is a phenotype determined by the localization, or where it reflects the activity of endometrial-like tissue at that site. Now we talk about function in a way that is similar to endometrium. Superficial endometrium is characterized by cyclic bleeding. Cyclic bleeding in peritoneal endometriosis leads to inflammatory reaction and fibrosis, and in the case of ovarian endometriosis it leads to adhesions and endometrioma formation. On the other hand, with rectovaginal endometriosis the fibromuscular proliferation reflects the activity that we see at the endometrial-myometrial junction.
Rectovaginal endometriosis has the morphological aspects of adenomyosis.
Therefore, today we can classify the phenotypes into two groups, one which is characterized by cyclic hemorrhage and the other predominantly by the smooth muscle metaplasia. I know that with laparoscopy you can easily see peritoneal endometriosis and ovarian endometriosis, but this is not the case with rectovaginal endometriosis. Pain is a very difficult problem because we know there are patients who have a lot of endometriosis and no pain, and there are patients who have very little endometriosis and a lot of pain. The classification system of the American Society for Reproductive Medicine is all right for infertility, but not for pain because that isn't the stage which reflects the pain. It may be more important to evaluate the lesions in terms of function or dysfunction rather than by the presence and extension of lesions.