It is the presence of endometrial tissue outside the uterus (ovaries, tubes, pelvis, abdomen, rectum, liver, bladder, etc). This tissue menstruates like a normal uterus but the blood is trapped in the pelvis leading to adhesions and pelvic scarring therefore possible delayed conception. The causes of endometriosis are still unknown but theoretical regurge of endometrial cells through the fallopian tubes and into the pelvis is one of the reasons.

Endometriosis

Endometrioma

Endometriosis