Current thinking on the pathogenesis of endometriosis.

This manuscript is a review of new ideas regarding the pathogenesis of peritoneal endometriosis, ovarian endometriosis, and retroperitoneal adenomyosis. Peritoneal endometriosis, the different aspects of which (black, red and white) represent distinctive steps in the evolutionary process, can be explained by the transplantation theory. Red lesions are the most active and most highly vascularized lesions and are considered to be the first stage of peritoneal endometriosis. The retroperitoneal nodule is an adenomyotic nodule whose histopathogenesis is not related to the implantation of regurgitated endometrial cells but to metaplasia of Müllerian remnants located in the rectovaginal septum. Metaplastic changes of Müllerian rests into adenomyotic glands involving the rectovaginal septum and the retroperitoneal space are responsible for the striking proliferation of the smooth muscle, creating an adenomyomatous appearance similar to that of adenomyosis in the endometrium.