Hydatidiform mole; complete v partial v choriocarcinoma v placental site tumour

Complete moles are usually 46.XX. This arises by fertilisation of an empty ovum by a spermatozoon which subsequently duplicates without cytogenesis. Less often, an empty ovum is fertilised by a diploid spermatozoon, which failed to undergo the second mitotic division. Partial moles are triploid, with two haploid genomes, arising because of dispermic fertilization of a haploid ovum with a defective zona pellucida.

Histology

Hydatidiform moles are abnormal gestations characterised by hydropic villi with circumferential hyperplasia or the villous trophoblast. Histological features of chorionic villi, such as partial involvement of villi by oedema and trophoblastic hyperplasia, irregular and scalloped borders of villi with deep infoldings, trophoblastic inclusions, and frequent microscopic evidence of fetal development have been suggested as characteristic findings of PHM. Fetal vessels are present in partial moles but usually absent from complete moles. However, morphology is inadequate to mark confident diagnoses in many cases3. Because complete mole is now commonly detected at a stage before the development of its classical diagnostic features, the histological features of complete mole at an early gestation are frequently confused with partial mole, hydropic miscarriage or non-molar chromosomal abnormalities. Flow and image cytometry are widely used to confirm the diagnosis.

Immunohistochemistry

	p57KIP2	hCG	placental alkaline phosphatase	hPL
partial mole	positive	weak	strong	variable
complete mole	negative	strong	weak	weak
choriocarcinoma	negative	strong	weak	weak
placental site tumour		focal	weak	strong

Greater reactivity for PCNA is seen in hydatidiform moles (complete or partial) than in hydropic abortions. All trophoblastic cell types are strongly immunoreactive for cytokeratins.

Prognosis

Moles may progress to persistent trophoblastic disease, placental site trophoblast tumour and choriocarcinoma. The incidence of persistent disease is far more common for complete moles (10-30%) than it is for partial moles (0.5-5%).

References

Brescia RJ et al. Immunocytochemical localisation of chorionic gonadotrophin, placental lactogen and placental alkaline phosphatase in the diagnosis of complete and partial hydatidiform moles. Int J Gynae Pathol 1987;6:213-229.

Jeffers MD et al. Comparison of villous trophoblast proliferation rate in hydatidiform mole and non-molar abortion by assessment of proliferating cell nuclear antigen (PCNA) expression. Placenta 1994;15:551-556.

3Fukunaga, M., S. Ushigome, et al. (1995). "Incidence of hydatidiform mole in a Tokyo hospital: a 5-year (1989 to 1993) prospective, morphological, and flow cytometric study." Hum Pathol 26(7): 758-64.

This page last revised 18.10.03.