is a pear-shaped organ roughly the size of a fist. The mucous membrane lining the uterus, known as the “endometrium”, plays a
major role in the development of endometriosis.
The mucous membrane of the uterus is formed in a cyclic fashion and is shed every month during menstrual periods. In most women, a little blood containing cells of the uterine mucous membrane passes via the fallopian tubes into the abdominal
cavity during periods. This phenomenon is known as retrograde or backward menstruation.
Depending on the appereance, a distinction is made between different stages of endometriosis. In mild endometriosis, there are a few endometriosis sites adhering to the outer wall of the uterus, to the tubes and the ovaries.
Cysts in which menstrual blood accumulates can form in the ovaries. If these cysts are opened up during an operation, this blood looks like a brownish, viscous mass. This is why these are also called “chocolate cysts”
Cyclic haemorrhages from endometriosis sites result in constant peritoneal irritation and subsequent formation of scar tissue (adhesions marked in green) and penetration of other adjacent tissues, such as the ligaments of the support apparatus, and other organs such as the bowel, bladder and ureter.