Endometriosis. Endoscope view of endometriosis on an ovary (white, centre). The endometriosis cyst is the small black lump next to the metal probe that is seen at upper left. Endometriosis is a condition where detached parts of the uterus's inner lining (endometrium) escape into the abdomen and attach themselves to internal organs. The lesions and cysts that result, bleed at the time of the menstrual cycle and cause great pain. The ovaries are the most commonly affected site. Usual treatments use drugs, though surgical reduction of the cyst (as here), using a thermoelectric probe or laser, may be required in severe cases, or where drugs fail to control the problem.