Histological examination shows placental tissue with large villi with stromal edema and marked trophoblastic proliferation (in a circumferential manner).

Hydatidiform moles are subdivided into complete and partial types (both can be invasive). Complete moles result from abnormal gametogenesis and fertilization. The trophoblastic cells contain only paternal chromosomes (androgenetic in origin). High prevalence in South East Asia. Clinically, there is raised serum hCG and the uterus is large for date. Grossly, it is described as “bunch of grapes”. Microscopically, the two important features of a complete mole are trophoblastic hyperplasia and vesicular swelling (cistern formation).

IHC: loss of p57 in cytotrophoblasts.

Treatment: Evacuation/curettage, and follow-up with serial serum human chorionic gonadotropin (hCG) levels, with or without prophylactic chemotherapy.

Incomplete moles, in contrast are triploid (69,XXX or 69,XXY). Microscopically, three of the below must be met for a diagnosis of incomplete moles:

- 2 populations of villi (large hydropic and smaller fibrotic)
- Enlarged, irregular, dysmorphic villi with trophoblast inclusions
- Enlarged villi with cisterns (at least 3 mm in size)
- Syncytiotrophoblast hyperplasia/atypia

IHC: p57+ in villous stromal cells and cytotrophoblast.

Treatment: Evacuation/curettage, and follow-up with serial serum human chorionic gonadotropin (hCG) levels.