Edematous villi > 2.5 mm for example at 10x, the full field is 2.2 mm so more than one field is concerning.
PHM: two populations of villi, mild to moderate circumferential trophoblastic proliferation trophoblastic hyperplasia but need to have hyperplasia to begin with. Cistern is helpful but not specific. But no villous inclusion.
CHM: one population, marked circumferential trophoblastic proliferation, abnormal distribution and loss of polarity like one side of the trophoblastic proliferation is exuberant. Villous inclusions are helpful. Can see cistern formation. Very early CHM poses a challenge: The villi may not be enlarged but have an irregular, bulbous or polypoid appearance, with hypercellular myxoid stroma (myxoid hue), prominent karyorrhexis, and trophoblast hyperplasia.
A review of pathogenesis of molar pregnancy is shown below:
Chromosome 11 contains CDKN1C (protein product is p57) – a paternally-imprinted maternally expressed gene.
Complete moles are diploid with only paternal copies of all genes on all chromosomes. One of the causes of Beckwidth-Wideman syndrome (and placental mesenchymal dysplasia) is uniparental disomy in which rather than having a paternal and maternal copy of chromosome 11, both copies of chromosome 11 are paternal – hence loss of p57.
CHM: 1. Sperm entered into an empty egg-sporadic androgenetic CHM
2. NLRP7 (NALP7) or KHDC3L mutations (familial biparental CHM)
leading to maternal imprinting. Uniparental disomy can also cause
biparental CHM.
PHM: 1. >95% are diandric triploidy
2. Monospermic/homozygous PHM due to failure of Meiosis I or Meiosis II
Case picture credit: https://www.virtualpathology.leeds.ac.uk/slides/library/view.php?path=%2FResearch_4%2FSlide_Library%2FR_Bishop_Collection%2FCard_index_Set%2FGynae%2F33666.svs
Screenshot credit: Atlas of Gynecologic Pathology: A Pattern-Based Approach by Dr. Tricia A. Numan, MD.
Main references:
hand-out from Dr.Omonigho Aisagbonhi, MD
Genotyping diagnosis of gestational trophoblastic disease: frontiers in precision medicine, Buza, Natalia et al. Modern Pathology, Volume 34, Issue 9, 1658 - 1672
Author: Wangpan Jackson Shi, MD
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