A 42-year-old woman underwent an endometrial curettage for dysfunctional bleeding. The curettings contained the tissue shown in this figure. Within the endometrium were sharply defined, eosinophilic nodules containing variably pleomorphic cells. Mitotic figures were not present and there was no necrosis.
What is your diagnosis?
This is an example of a placental site nodule or plaque, also known as a subinvoluted implantation site. The nodule consists of chorionic-type intermediate trophoblasts embedded in an eosinophilic fibrillar background matrix. The nodule is typically sharply demarcated from the surrounding endometrium and superficial myometrium. The trophoblastic cells with stain strongly for low molecular weight cytokeratins (CK 8/18). Staining for human placental lactogen (HPL) is typically focal and staining for beta-HCG is usually absent. In contrast to proliferative lesions of intermediate trophoblasts, the Ki-67 labelling index should be essentially zero.
Placental site nodule should be distinguished from proliferative trophoblastic lesions including exaggerated placental site reaction, placental site trophoblastic tumor, and epithelioid trophoblastic tumor. The small size and sharp circumscription usually allow ready distinction and, if necessary, the low (zero) Ki-67 index will also be helpful. Placental site nodule may also be confused with squamous cell carcinoma and this confusion may be aided by the cytologic atypia and cytokeratin positivity of placental site nodule. Again, the small size and lack of mitotic activity / Ki-67 index should allow ready distinction.
Placental site nodules have been thought to represent residua of prior pregnancy. They may persist for years. Occasionally they are found in patients with no known history of pregnancy and may well represent a blighted gestation that never fully developed and was unrecognized by the patient. Regardless, the lesion requires no further therapy and is adequately treated by the curettage (or hysterectomy) that led to its diagnosis.