Placental site nodule occurring in a fallopian tube.

The placental site nodule (PSN), a recently described benign lesion of intermediate trophoblast, is usually an incidental finding in younger women. It is a well-circumscribed, round to oval lesion that is extensively hyalinized and immunohistochemically stains for cytokeratin, placental alkaline phosphatase (PLAP), human placental lactogen (HPL) and, focally, for human chorionic gonadotropin (HCG) and epithelial membrane antigen (EMA). Thus far, the cases reported have been found in endometrial curettage or hysterectomy specimens. The pathogenesis of PSN is yet to be ascertained; however, there is wide acceptance of the fact that it represents a remnant of the placental implantation site. If this is indeed the case, it should not be surprising to find PSN occurring at sites of ectopic gestation. We describe herewith a case in which PSN was found in a fallopian tube segment resected in a postpartum tubal ligation.