**14. Microscopic features of endometriosis**

Typically endometriosis in women of reproductive age presents histologically as one or more endometrioid glands surrounded by stromal cells, resembling the endometrial stromal cells of the proliferative phase. The glandular epithelium is one layer thick with cuboidal or tall cells and eosinophilic cytoplasm. Nuclei are ovoid with vertical orientation and very rare mitoses. The whole picture is usually consistent with inactive or irregular proliferative endometrium, although typical proliferative or secretory changes may be observed. Cilia may be observed as well. Stromal cells are supported by a delicate reticulin network in which hyperemic small vessels may be observed. In the case of exogenous administration of progestins, cyclically functionic endometriosis or pregnancy, a stromal decidual reaction may be observed. A diffuse infiltration of histiocytes is usually observed. The histiocytes convert the red blood cells into glucolipid and brown pigment (pseudoxanthoma cells) .The pigment is usual a ceroid such as lipofuscin and to a lesser extend hemosiderin .The amount of the pigment increases with the age of the lesion. Inflammatory cells may be present and a small component of smooth muscle cells especially in the wall of endometrioid cysts may be observed. Not all the above described elements are easily identified in endometriosis. Especially in the cases of ovarian endometrioid cysts the lesion appears to be composed of stroma, with fibrosis, lined by hemosiderin-laden macrophages. Many histological sections may be necessary to identify the glandular component of endometriosis. One must keep in mind that macrophages may be connected with hemorrhagic follicles or corpora lutea and only the presence of glandular epithelium or luteinized cells is diagnostic. The degree of cyclic changes of the glandular component depend on the amount of fibrous tissue, the amount of stroma round the glands, the degree of vascularity and the steroid receptor content Endometriosis in places with native smooth muscle component may induce marked hypertrophy identical to that observed in cases of adenomyosis that leads to creation of adenomyomata or adenomyomatous nodules (Anaf et al, 2000).
