Placental vascular malformation with mesenchymal hyperplasia and a localized chorioangioma. A rarity simulating partial mole.

We here report a case of placental vascular malformation with mesenchymal hyperplasia of the villi and a localized chorioangioma. After an uneventful pregnancy our patient delivered a non-malformed live female infant. The placenta was grossly enlarged, and macroscopically it was characterized by strongly enlarged varicous chorionic vessels. On the maternal plate vesicle-like structures, giving the impression of partial mole, were seen. At microscopy level, areas of normal looking tissue alternated with areas of excessively enlarged villi, in which the ground substance contained large amounts of acid mucopolysaccharide, corresponding to "mesenchymal hyperplasia". Moreover, a localized chorioangioma was found. In none of the histological sections were cisterns, abnormal trophoblastic proliferation, stunted ramification or stromal trophoblastic inclusions observed. In week 15 maternal se-AFP was elevated to 3.03 multiples of the median. Genetic analyses revealed a normal female karyotype and biparental genomic contributions to 7 unlinked loci. Placental vascular malformation with mesenchymal hyperplasia is a differential diagnosis to partial mole which should be considered when vesicle like placental enlargement is observed along with a living fetus.