5 - The myometrium

Summary

Non-neoplastic conditions of the myometrium

ADENOMYOSIS

Adenomyosis is characterised by the presence of endometrial tissue deep within the myometrium and there is almost invariably an associated hypertrophy of smooth muscle around the ectopic islands of endometrium. The foci of endometrial tissue may be distributed diffusely within the myometrium, in which case the uterus shows a roughly symmetrical enlargement, or can be focal, forming a poorly-defined tumour-like asymmetrical thickening of the myometrium (Figure 5.1). The localised form is often known as an ‘adenomyoma’, an unfortunate term because of its misleading connotation of neoplasia. Histologically, foci of adenomyosis consist of both endometrial glands and stroma (Figure 5.2). The glands are usually of basal type and thus do not show cyclic activity.

Adenomyosis is caused by a downgrowth of basal endometrium into the myometrium. Serial sectioning shows continuity between the basal endometrium and foci of adenomyosis. The aetiology of this diverticular disease is, however, obscure, for although both curettage and estrogenic stimulation have been proposed as aetiological factors, there is no proof that either is of causal significance.

VASCULITIS

The majority of cases of vasculitis of the myometrium are isolated lesions, particularly when they affect only the small vessels. Occasionally, however, larger arteries are affected and the possibility of there being a systemic arteritis should be considered.

INFLAMMATION

Infection in the endometrium may spread to the myometrium following childbirth, miscarriage or intrauterine surgery. On rare occasions, however, non-infective inflammation may develop in systemic disease, such as sarcoidosis (Figure 5.3).