Uteruslike mass of the ovary: endomyometriosis or congenital malformation? A case with a discussion of histogenesis.

We describe an 18-year-old woman with a mass in the region of the right ovary. The mass, which had a central cavity lined by endometrium and surrounded by smooth muscle, extraordinarily resembled a uterus. Review of the literature disclosed only one such case in which this change was considered to arise from endomyometriosis of the ovary, a phenomenon characterized by smooth-muscle metaplasia in a focus of endometriosis. Although this possibility is interesting and plausible, we believe that a congenital malformation, possibly caused by a defect in fusion of müllerian ducts, should strongly be considered in explaining the pathogenesis of this kind of lesion.