When endometrial glands and stroma are found outside the uterus, the condition is known as endometriosis. Up to 10% of women may have this condition. It can be very disabling and painful, even when just a few foci are present. Diagrammed here are typical locations for foci of endometriosis. Sometimes the old dark brown blood collects over time from repeated hemorrhage in a cystic space in the ovary and produces a so-called "chocolate cyst".

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