The inside of the uterus is lined with tissue called the endometrium. The endometrium thickens in response to hormones produced during the monthly menstrual cycle. As hormone levels fall, the lining is shed and passed as the menstrual period.
Endometriosis is a disease in which endometrial tissue is found outside the uterine cavity. The common sites for these abnormal deposits are the peritoneal (outer) surfaces of the reproductive organs (uterus, fallopian tube and ovaries) and the rest of the pelvic cavity.2 In severe cases these may be found over the bowel or bladder.
The endometriotic deposits respond to hormones and undergo cyclical changes similar to the endometrium. As a result of cyclical bleeding from these ectopic (misplaced) endometriotic implants, a local inflammatory reaction occurs. This eventually leads to scarring, with adjacent organs becoming adherent. In some patients large collections of blood may accumulate, especially in the ovary.
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