What is endometriosis primarily characterized by?

Endometriosis is primarily characterized by the growth of uterine tissue outside the uterus. This condition occurs when endometrial-like tissue, which normally lines the inside of the uterus, begins to develop in areas such as the ovaries, fallopian tubes, the outer surface of the uterus, and other organs within the pelvis. This abnormal tissue growth can lead to inflammation, pain, and the formation of scar tissue, significantly impacting a person's quality of life.

The other choices may be associated with symptoms or complications related to endometriosis but do not define the condition itself. While the presence of ovarian cysts can occur in women with endometriosis, these cysts (often called endometriomas) are a consequence rather than the key characteristic. Hormonal imbalances can contribute to the severity of symptoms but are not the defining feature of the disease. Menstrual irregularities may be symptoms experienced by individuals with endometriosis, but again, they do not encapsulate the essence of the condition like the growth of uterine tissue outside the uterus does.