Ovarian prostatic tissue originating from hilar mesonephric rests.

Nonteratoid prostatic differentiation in the ovary of a parous, phenotypically normal, postmenopausal woman is reported for the first time, to the authors' best knowledge. The patient was a 70-year-old woman who underwent bilateral oophorectomy following pelvic ultrasound examination that showed enlargement of the left ovary and an equivocally abnormal Doppler signal. Histologic examination showed a normal right ovary and a left ovary enlarged by hilar cystic dilatation related to a proliferation of mesonephric remnants exhibiting various types of epithelial metaplasia, including hyperplastic rete and epididymal-like and clear cell epithelia resembling the lining of the seminal excretory system. These were closely associated, occasionally even merging, with a discrete area of prostatic acinar and smooth muscle differentiation in the cyst wall. The identity of the prostatic tissue was confirmed immunohistochemically by positive staining with prostate specific antigen and prostatic acid phosphatase. The lesion was associated with an incidental, microscopic hemangioma. A developmental malformative origin of this abnormality cannot satisfactorily be explained by current embryologic concepts. A hypothesis of a metaplastic induction of prostatic tissue by mesonephric remnants is proposed, since complex metaplastic changes coexisted within the cysts and even showed epithelial transitions with the prostatic acini.