Benign endometrial glands without architectural complexity or cytologic atypia are surrounded by stroma that consists predominantly of smooth muscle. This lesion presented as a polyp projecting into the endometrial cavity.
Grossly, in areas of endometriosis the blood is darker and gives the small foci of endometriosis the gross appearance of "powder burns". Small foci are seen here just under the serosa of the posterior uterus in the pouch of Douglas. Such areas of endometriosis can be seen and obliterated by cauterization via laparoscopy.
Upon closer view, these five small areas of endometriosis have a reddish-brown to bluish appearance. Typical locations for endometriosis may include: ovaries, uterine ligaments, rectovaginal septum, pelvic peritoneum, and laparotomy scars. Endometriosis may even be found at more distant locations such as appendix and vagina.
This is a section through an enlarnged 12 cm ovary to demonstrate a cystic cavity filled with old blood typical for endometriosis with formation of an endometriotic, or "chocolate", cyst. The hemorrhage from endometriosis into the ovary may give rise to a large "chocolate cyst" so named because the old blood in the cystic space formed by the hemorrhage is broken down to produce much hemosiderin and a brown to black color.
