Mullerian papilloma-like proliferation arising in cystic pelvic endosalpingiosis

This report describes an unusual epithelial proliferation occurring in pelvic cystic endosalpingiosis. A cyst mass lined by a layer of ciliated epithelial cells involved the posterior surface of the cervix and vagina. The epithelial proliferation within the wall resembled a mullerian papilloma with fibrous and fibrovascular cores lined by bland cuboidal epithelial cells. Other areas had a microglandular growth pattern resembling cervical microglandular hyperplasia, and focally there was a solid growth pattern. Foci of typical endosalpingiosis involved the surface of both ovaries and pelvic soft tissues. The cystic lesion recurred after partial cystectomy and drainage and was followed up radiologically and with periodic fine-needle aspiration. Part of the wall of the cyst removed 11 years after the original surgery showed an identical epithelial proliferation. MIB1 staining showed a proliferation index of less than 5%, contrasting with the higher proliferation index of a typical serous borderline tumor. The differential diagnosis is discussed. As far as we are aware, this is the first report of such a benign epithelial proliferation involving cystic endosalpingiosis.