An endometrioma is a mass of tissue (noncancerous cyst or tumor) that contains shreds of endometrial tissue. Endometriomas most frequently occur in the ovary, in a part of the peritoneum (sac around the internal organs) between the rectum and uterus, the wall (septum) between the rectum and vagina, and the outside of the uterus.

Jan 19th, 2026 10:29 PM