Endometrioma is the presence of endometrial tissue in and sometimes on the ovary. It is the most common form of endometriosis. Endometrioma is found in 17–44% patients with endometriosis. Endometriomas are typically an advanced form of endometriosis, around stage three or four. More broadly, endometriosis is the presence of 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