Peritoneal endometriosis, ovarian endometriosis, and adenomyotic nodules of the rectovaginal septum are three different entities.

OBJECTIVE: To review the histogenesis of peritoneal, ovarian, and rectovaginal endometriotic lesions.
DESIGN: The comparison of morphologic, morphometric, and histochemical data observed in each type of lesion.
SETTING: A university hospital department of gynecology. PATIENT(S): Patients complaining of infertility or pelvic pain with laparoscopically proved endometriosis. INTERVENTION(S): Laparoscopy was performed, and biopsy specimens from the endometriotic lesions were histologically studied. RESULT(S): Three types of endometriotic lesions must be considered: peritoneal, ovarian, and rectovaginal. Morphologic and morphometric data show similarities between eutopic endometrium and red peritoneal lesions, suggesting that these lesions are the first stage of early implantation of endometrial glands and stroma. After partial shedding, the red lesions regrow constantly. The shedding induces an inflammatory reaction, provoking scarification, and the lesions become black. The subsequent fibrosis leads to areas of white opacification that are inactive. The pathogenesis of ovarian endometriomas is a source of controversy. Although there seems to be a consensus concerning the invagination theory, there is still a contradiction between the implantation theory and the metaplasia theory. We recently showed that the mesothelium covering the ovary can invaginate into the ovarian cortex, pushing back the primordial follicles. The presence of mesothelial invagination in continuum with endometriotic tissue suggests that metaplastic histogenesis of ovarian endometriotic lesions occurs. Rectovaginal endometriotic nodules must be considered adenomyomas, consisting of smooth muscle with active glandular epithelium and scanty stroma. Immunocytochemical results show poor differentiation and hormonal independence of these lesions and indicate a close relation with their mesodermal müllerian origin. CONCLUSION(S): Peritoneal, ovarian and rectovaginal endometriotic lesions must be considered as three separate entities with different pathogeneses.