Complete hydatidiform mole histology

(A) Enlarged, cavitated chorionic villi (CV) are the hallmark of "classic" complete hydatidiform mole. Florid, circumferential trophoblast hyperplasia (arrows) also distinguishes complete from partial moles and nonmolar gestations.

(B) Immunohistochemistry for p57 is a useful tool for confirmation of complete mole, especially in diagnostically challenging cases. Brown staining product is not found in villous cytotrophoblasts (arrows) and stromal nuclei due to silencing of paternal alleles during imprinting. This silencing is relaxed in extravillous trophoblast (bottom of panel B), which is used as a positive internal control for p57 immunostaining.

(C) In early complete hydatidiform mole, villous cavitation has not yet developed, but other notable features allow histopathological diagnosis. The villi of early complete mole often have deep, narrow cleft-like invaginations of the trophoblast surface, resembling "toes" or "popcorn." The precavitated stroma is basophilic (blue) and contains degenerating cells with karyorrhexis.