New diagnostic modalities in the histopathological diagnosis of hydatidiform moles

Hydatidiform moles represent a fascinating group of trophoblastic proliferative disorders with unique genetic compositions and often challenging morphologic features for diagnosis. While conventional histomorphology remains the cornerstone of the diagnosis of molar gestations, there has been an ongoing search for the past three decades for new diagnostic modalities to aid the pathologist. In this review first we will discuss the histopathologic features of molar gestations and their mimics, including non-molar hydropic abortions, chromosomal trisomy syndromes, digynic non-molar triploidy and placental mesenchymal dysplasia. Then we will focus on the conventional and novel ancillary techniques – ploidy analysis, fluorescent in situ hybridization, immunohistochemistry and molecular genotyping – and their role in the diagnostic algorithm.