Placenta, partial hydatidiform mole, p57 stain

Partial hydatidiform mole is a product of conception with abnormal chorionic villi due to a chromosomal abnormality (triploidy). This can arise, for example, with fertilization by two sperm. Partial mole is characterized by two populations of villi; sclerotic and enlarged. The latter shows scalloped borders and trophoblastic inclusions with lacy proliferation of syncytiotrophoblasts. Unlike a complete mole, which lacks maternal DNA, partial moles show retention of the maternally expressed p57 protein in stromal villous cells and cytotrophoblast.