What medical condition is characterized by the presence of endometrial tissue outside the uterus?

Endometriosis is a medical condition defined by the growth of endometrial-like tissue outside the uterine cavity. This tissue can be found on the ovaries, fallopian tubes, the outer surface of the uterus, and other organs within the pelvis. Endometriosis can lead to a variety of symptoms, including pelvic pain, especially during menstruation, heavy menstrual bleeding, and infertility, as the ectopic tissue responds to hormonal changes in the same way as normal endometrial tissue.

In contrast, polycystic ovary syndrome is primarily an endocrine disorder that affects ovarian function and is characterized by irregular menstrual periods, excess androgen levels, and polycystic ovaries, but it does not involve the presence of endometrial tissue outside the uterus. Fibroids refer to benign tumors in the uterus, composed of smooth muscle and fibrous tissue, that do not imply the presence of endometrial tissue outside its normal location. Conversely, pelvic inflammatory disease is an infection of the female reproductive organs, often caused by sexually transmitted infections; it may involve inflammation of the uterus, ovaries, and fallopian tubes, but it does not involve ectopic endometrial tissue.

Thus, the defining characteristic of endometriosis is the presence of