"Most commonly adenomyosis is mistaken for another common condition, uterine fibroids. There is however a fundamental difference between a fibroid (a distinct tumor) and adenomyoma. Each fibroid originates from one abnormal cell. Under the effect of estrogen this cell multiplies. The growing tumor may displace and compress tissues but it does not invade the surrounding uterine muscle. Because of this growth pattern of fibroids, it is possible to remove all of the tumor without removing any normal uterine tissue during myomectomy (surgical removal of fibroids). In contrast, adenomyoma is not a discrete tumor but rather a local swelling of the uterine wall as a result of the penetration of endometrial tissue. Therefore it is not possible to remove tissue affected by adenomyosis without actually removing the involved uterine muscle." http://www.adenomyosis.org/#WhatisAdenomyosis