An abnormal condition of the uterus in which glands from the endometrium grow into the muscle of the wall of the uterus (the myometrium), causing local or general enlargement of the uterus, pain with periods, and perhaps heavier periods. A localised area of adenomyosis is called an adenomyoma and can be hard to distinguish from a fibroid on transvaginal ultrasound, although an increase in the serum CA 125 antigen level can point to the correct diagnosis. Unlike a fibroid it is not easily removed at surgery, because it's not clearly separable from surrounding tissue. There's no satisfactory long term treatment for adenomyosis: hysterectomy may be chosen if symptoms are bad enough. GnRH-agonists give just temporary relief.

A mucus-like protein produced in some circumstances by surface cells of tissues derived from the Mullerian ducts. Its function is obscure but measurement as serum CA125 antigen can be useful in diagnosing adenomyosis, endometriosis and some cancers of the ovary.

Painful menstruation. Can be primary, present in teenagers, generally in spasms around the start of the period; or it can be secondary, developing as a woman gets older, and then typically lasting more than a day or so into the period, with prolonged aching as well as spasms. Primary dysmenorrhea might have no medical importance beyond the suffering the pain causes, and typically gets better as a woman reaches her 20s; severe or persistent cases, however, warrant investigation. Secondary dysmenorrhea can signify, for example, endometriosis, fibroids, adenomyosis or peritubal adhesions.

Measurement of CA125 antigen in serum. A test done to investigate, particularly, adenomyosis and cancer of the ovary. Levels can also be increased with endometriosis (especially when there is a 'chocolate cyst' present), during normal menstruation and during normal early pregnancy.