What is the difference between adenomyosis and endometriosis?

Location: Endometriosis is the presence of the cells that line the inside of the uterus in areas outside the uterus, such as the ovaries, the lining of the abdominal cavity called the peritoneum, or pretty much anywhere else. Adenomyosis is the presence of the lining cells in the muscle of the uterus itself.

Location of lesions: Endometriosis is the presence of tissue that looks like the endometrium (the lining of the uterine cavity) outside the uterus, in the pelvic or abdominal cavities. Adenomyosis is when implants of endometrial tissue are found within the myometrium which is the muscular walls that make up the corpus, or body, of the uterus itself. Adenomyosis often causes heavy periods, while endometriosis doesn't.

Same process: The uterus is made up of a thin lining and a much thicker muscular portion. The lining is called the endometrium. When these cells are found outside the uterus, it is endometriosis. When these lining cells are located deep to the lining but still inside the uterus that is adenomyosis. Simply put, adenomyosis is endometriosis that involves the uterus (below the lining).