Adenomyosis is the non-neoplastic (benign) invasion of endometrium into the myometrium of the reproductive female. It is a relatively common disorder (15-30% of resected uteri), but causes symptoms in only a small percentage of patients, usually late in the reproductive years. Abnormal genital tract bleeding such as menorrhagia and metrorrhagia are the most common complaints, followed by nonspecific pelvic pain and bladder and rectal pressure. On examination, the patient may have a large uterus.
Upon gross pathological examination, the uterus is enlarged by a diffuse process, and the myometrium is thick, trabecular, and may be cystic. Microscopically, endometrial tissue can be found deep in the myometrium, and is usually usually more than 1/4 of the wall's thickness. Also, there is smooth muscle hypertrophy.