Adenomyosis

Adenomyosis is a benign condition in which endometrial glands and stroma are found within the myometrium, the muscular wall of the uterus. The surrounding muscle typically becomes hypertrophied, and the uterus is often diffusely enlarged. It commonly presents with heavy menstrual bleeding and painful periods, frequently in the later reproductive years.

Definition

Adenomyosis is the presence of ectopic endometrial glands and stroma within the myometrium, accompanied by adjacent smooth-muscle hypertrophy and, frequently, diffuse uterine enlargement.

Scope

This entry covers adenomyosis as a benign clinical entity: its definition, the main hypotheses about how endometrial tissue comes to reside within the myometrium, its relationship to neighboring conditions, and its typical presentations. It is a reference overview and does not provide treatment recommendations.

Core questions

• How does endometrial tissue come to lie within the uterine muscle in adenomyosis?
• How is adenomyosis distinguished from uterine fibroids and from endometriosis?
• Why is adenomyosis associated with heavy menstrual bleeding and dysmenorrhea?

Key concepts

• Ectopic endometrium within the myometrium
• Endometrial-myometrial junctional zone
• Myometrial smooth-muscle hypertrophy
• Diffuse versus focal (adenomyoma) forms
• Heavy menstrual bleeding and dysmenorrhea
• Frequent coexistence with fibroids and endometriosis

Key theories

Invagination of the endometrial-myometrial junction

A leading hypothesis holds that the basal endometrium invaginates downward into the myometrium, especially where the endometrial-myometrial junctional zone is disrupted, establishing ectopic glands within the muscle. A competing view proposes de novo metaplasia of displaced or embryonic cell rests within the myometrium.

Mechanisms

The dominant model is invagination of basal endometrium into the underlying myometrium, often linked to disruption or altered function of the endometrial-myometrial junctional zone; an alternative model proposes metaplastic formation of endometrial tissue from displaced or embryonic cell rests within the muscle. Once established, ectopic glands and the surrounding hypertrophied, often poorly contractile muscle are thought to contribute to heavy menstrual bleeding and to dysmenorrhea. Adenomyosis frequently coexists with fibroids and with endometriosis, which can complicate its recognition.

Clinical relevance

Adenomyosis is a common cause of heavy menstrual bleeding and dysmenorrhea and is included as a structural cause within the FIGO PALM-COEIN classification of abnormal uterine bleeding. Its diagnosis has historically depended on histology of the uterus, with imaging increasingly used to identify it. This entry describes the condition for reference purposes and is not a basis for individual diagnostic or treatment decisions.

Epidemiology

Reported prevalence of adenomyosis varies widely because estimates have depended heavily on the diagnostic method and on the population examined, including historical reliance on hysterectomy specimens. It is most often recognized in the later reproductive years and frequently coexists with other benign uterine conditions.

History

Adenomyosis was historically described from pathology of removed uteri and was once termed 'endometriosis interna,' reflecting an assumed kinship with endometriosis; the two are now regarded as distinct though sometimes coexisting entities. Advances in imaging shifted recognition away from reliance on surgical specimens, and contemporary reviews have re-examined the competing invagination and metaplasia hypotheses for its origin.

Debates

Invagination versus metaplasia as the origin of adenomyosis

Whether adenomyotic lesions arise mainly from downward invagination of basal endometrium across a disrupted junctional zone or from metaplasia of displaced or embryonic cells within the myometrium remains unresolved, and the two mechanisms may not be mutually exclusive.

Seminal works

• garcia-solares-2018

Frequently asked questions

How is adenomyosis different from endometriosis?

In adenomyosis, endometrial-type tissue is located within the muscular wall of the uterus itself, whereas in endometriosis it is found outside the uterus, such as on the pelvic peritoneum or ovaries. The two are distinct conditions that can occur together.

Is adenomyosis cancer?

No. Adenomyosis is a benign condition. It can cause heavy, painful periods and uterine enlargement, but it is not malignant.