Endometriosis happens when the endometrium, the tissue that usually lines the inside of a woman’s uterus, grows outside it.
This tissue acts like regular uterine tissue does during your period: It will break apart and bleed at the end of the cycle. But this blood has nowhere to go.
Surrounding areas may become inflamed or swollen. You might have scar tissue and lesions.
Endometriosis is most common on your ovaries.
Types of Endometriosis
There are three main types of endometriosis, based on where it is:
Superficial peritoneal lesion. This is the most common kind. You have lesions on your peritoneum, a thin film that lines your pelvic cavity.
Endometrioma (ovarian lesion). These dark, fluid-filled cysts, also called chocolate cysts, form deep in your ovaries. They don’t respond well to treatment and can damage healthy tissue.
Deeply infiltrating endometriosis. This type grows under your peritoneum and can involve organs near your uterus, such as your bowels or bladder. About 1% to 5% of women with endometriosis have it.
