Case 1: Hyalinization and fibrinoid deposition with embedded degenerating trophoblastic cells are the key features of a placental site nodule. In this case, the lesion is more plaque-like than nodular.
Case 2: A hyalinzed nodule consisting of trophoblasts is seen in a background of proliferation endometrium with glandular and stromal breakdown.
A placental site nodule (PSN) is a small benign circumscribed lesion composed of retained extravillous trophoblastic tissue. The nodule may be found anywhere from several weeks to years after a pregnancy.
They are usually too small to be detected by the naked eye. If visible, they are pale-tan nodules which may be hemorrhagic, ranging 1-4 mm in diameter. The preferred anatomic site is the lower uterine segment or cervix. Microscopically, the nodule is well-circumscribed and nodular. Sometimes, it is less globoid and more plaque-like. Degenerate intermediate trophoblasts are embedded in a hyalinized matrix and abundant fibrinoid deposition.1
The trophoblastic cells in a PSN are immunoreactive for EMA, keratin, PLAP and inhibin. The key differential diagnosis would be a placental site trophoblastic tumor (PSTT). Placental site nodules are more circumscribed and hyalinized compared to the infiltrative nature of a PSTT. Mitotic activity and Ki-67 labeling index is low in PSN, whereas PSTT is mitotically active with a high Ki-67 index.2
Occur in reproductive age women, however, the preceding pregnancy may be remote. Usually an incidental finding and rarely, some patients may present with abnormal bleeding.
Treatment is with endometrial curettage.
While there is no progression to malignancy, patients may experience some reproductive difficulties and menstrual irregularities which usually resolve with removal.
1 Baergen RN. Manual of Benirschke and Kaufmann's Pathology of the Human Placenta. New York, NY: Springer; 2005: 448-9.
2 Mazur MT, Kurman RJ. Diagnosis of Endometrial Biopsies and Curettings. New York, NY: Springer; 2005: 54-5.