Endometrioma is the presence of tissue similar but distinct to the endometrium in and sometimes on the ovary. It is the most common form of endometriosis. Endometrioma is found in 17–44% patients with endometriosis. More broadly, endometriosis is the presence of tissue similar but distinct to endometrial tissue located outside the uterus. The presence of endometriosis can result in the formation of scar tissue, adhesions and an inflammatory reaction. It usually is a benign growth. An endometrioma is most often found in the ovary. This ovarian endometriosis forms dark, fluid-filled cysts. These fluid-filled sacs can vary greatly in size and are known as endometriomas, also called "chocolate cysts". The fluid inside the cysts is thick, dark, old blood, giving it a chocolate-like appearance. It can also develop in the cul-de-sac (the space behind the uterus), the surface of the uterus, and between the vagina and rectum. Pathophysiology
Endometrial tissue is the mucous membrane that normally lines the uterus. The endometrium is richly supplied with blood and its growth is regulated by estrogen and progesterone. It consists of glandular and stroma tissue from the lining of the uterus. When the endometrial mucous membrane is found outside of the uterus in places such as the ovaries, it causes chronic pelvic pain with intercourse and menstrual cycles. Endometriomas can produce a toxic environment by producing estrogen, cytokines, interleukins, and other inflammatory substances, that could damage healthy endometriomal tissue.
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