Introduction

Endometriosis is usually a painful disorder of the female reproductive system. In endometriosis, a specialized type of tissue that normally lines the inside of your uterus (the endometrium) becomes implanted outside your uterus, most commonly on your fallopian tubes, ovaries or the tissue lining your pelvis. Rarely, endometrial tissue may spread beyond your pelvic region.

During your menstrual cycle, hormones signal the lining of your uterus to thicken to prepare for possible pregnancy. If a pregnancy doesn't occur, hormone levels decrease, causing the thickened lining of your uterus to shed. This produces bleeding that exits your body through the vagina — your monthly period.

When endometrial tissue is located elsewhere in your body, it continues to act in its normal way: It thickens, breaks down and bleeds each month as your hormone levels rise and fall. Because there's nowhere for the blood from this displaced tissue to exit your body, it becomes trapped, and surrounding tissue can become irritated.Trapped blood may lead to the growth of cysts.

Cysts, in turn, may form scar tissue and adhesions — abnormal tissue that binds organs together. This process can cause pain in the area of misplaced tissue, often the pelvis, especially during your period. Scars and adhesions related to endometriosis also can cause fertility problems.

Endometriosis isn't the only cause of pelvic pain. If you're experiencing pelvic pain, see your doctor to determine whether endometriosis or another condition is the cause, and to target appropriate treatment.