Hydatidiform mole: cytogenetically unusual cases and their implications for the present classification.

Unusual observations in hydatidiform moles are of clinical importance as well as of theoretical interest when the present subgrouping into partial or complete moles is evaluated, particularly in view of the more malignant potential of the latter. The purpose of the present review is to summarize, update, and evaluate information on moles with unusual karyotypes or origins. The important factor in the evolution of partial or complete moles appears to be the ratio of maternal to paternal chromosomes and not the ploidy of the tissue. Complete hydatidiform moles develop from androgenetic conceptions while partial hydatidiform moles develop from those conceptions in which the number of paternal sets of chromosomes exceeds the number of maternally derived sets. Rare cases inconsistent with this concept emphasize the value of examining morphologic features, cell ploidy, and genetic markers when one is attempting to classify hydatidiform moles.