There are three major theories for its etiology. The first is that implantation of endometrial tissue happens due to retrograde menstrual flow along the uterine tubes to the peritoneum, which occurs regularly in the normal reproductive female. The second is that metaplasia causes peritoneal cells to change to endometrial tissue. The third is that there is vascular or lymphatic spread.
Endometriosis is an important clinical condition that affects 10% of women between 20 and 40. Symptoms include acquired pain (during menses, pelvic or back pain), infertility (30-40%), dysuria, painful defecation, dyspareunia, and abnormal genital tract bleeding.
The gross pathological appearance is variable, depending on the site and duration of the disorder. In early cases, there are white or red punctate foci, patches or nodules, as well as red, blue, or brown "powder" burns. In extensive cases, the adhesions are dense, especially in the uterine tubes and ovaries (hence infertility), and in the pouch of Douglas (hence pain). In cases where the endometriosis is on the ovaries, the cystic spots are called endometriomas (aka chocolate cysts). The ovarian wall is also fibrous, and the ovary contains degenerated blood contents.
Diagnosis happens on confirmation of two of three features: endometrial glands; endometrial stroma; and hemosiderin. Diagnosis can be made on biopsies or resected foci early in the disease course, but not necessarily in long standing "burned out" cases.