The endometrial identity of benign stromatosis of the ovary and its relation to other forms of endometriosis.

A series of 114 ovaries form women aged 20 to 82 showed cortical islands of endometrial stroma in about two-thirds of those over 40. This identity was commonly apparent in ordinary sections and was confirmed in half the affected ovaries by the presence of K cells (endometrial granulocytes) in one or more foci; it may be masked by attenuation or conversion into smooth muscle. The islands show transitional forms to decidual foci and to cortical granulomata and related leucocytic lesions, a few of which also showed K cells: they are ultimately converted into weakly orceinophil hyaline foci which are common in later life and showed K cells in four instances and continuity with stromal islands in 20 ovaries. The lesions appear to arise from the implantation of endometrial stroma into the ovary, the surface of which becomes more cellular and probably more permeable after 40. The islands may foster the development of cortical stromal hyperplasia and their antecedents that of surface epithelial tumours.