The introduction of an intrauterine device into the uterine cavity induces a foreign body reaction in the surrounding endometrium which is characterized by the infiltration of polymorphonuclear leucocytes and macrophages into the endometrial stroma and subsequently through the surface epithelium. Leucocyte migration is greater with copper IUDs than with inert IUDs. Ulceration of the surface epithelium, haemorrhage of erythrocytes and microthrombosis of stomach capillaries occur in the functional endometrium in contact with inert and copper IUDs. In endometrium adjacent to, but not in contact with, the IUD gaps appear in the endothelial lining of small blood vessels without a haemostatic response. The most striking response in endometrium exposed to progesterone-releasing IUDs is the occurrence of dilated, thin-walled vesicles, associated with a thinning of the surface epithelium and a decidual reaction in the stroma. A uniform suppression of the endometrium in progesterone IUD users is always found after six months of treatment, whereas the insertion of IUDs releasing 20-30 micrograms levonorgestrel induce a profound uniform suppression of the functional endometrium throughout the uterus after only four weeks.
PIP: This is a descriptive review of the histological changes in the endometrium in the presence of IUDs: inert, copper, progesterone and levonorgestrel-releasing IUDs. All IUDs evoke a foreign body reaction to some degree, and trauma at the sites where the IUD bears on the surface of the endometrium. The foreign body reaction is an inflammatory response characterized by infiltration of leukocytes and macrophages throughout the endometrial tissue, the intrauterine space and on the IUD surface. Copper IUDs stimulate more leukotaxis, principally of PMN leukocytes. At the site of impression of the IUD, endometrial surface layers are eroded down to the basement membrane, more so with larger IUDs. There are defects in vascular epithelium, hemorrhages unchecked by hemostasis, and also direct bleeding from the ulcerated areas in contact with the IUD. Progesterone medicated IUDs elicit a decidual reaction and a thinning of the surface endometrium associated with distinctive dilated, thin-walled vesicles, a response that becomes stable over 6 months, according to the dose of progesterone released. Levonorgestrel-releasing IUDs, in contrast, produce a profound, uniform suppression of cyclic gland and endothelium development within 1 month. Clinically, levonorgestrel IUDs cause less spotting. No dysplastic or malignant changes have been reported under the influence of IUDs, and normal structure and function of the endometrium returns about a month after an IUD is removed.