Ilana Ariel1, Debra Goldman-Wohl2, Efraim Gazit3, Ron Loewenthal3, Simcha Yagel2
The Department of 1Pathology and 2The Center for Human Placenta Research, Department of Obstetrics and Gynecology, Hadassah-Hebrew University Medical Center, and 3The Laboratory for Tissue typing, Chaim Sheba Medical Center
Introduction: a comprehensive study of unusual cases of placental pathology can reveal insights into flaws in processes of human fertilization. A G3P2 39-year-old woman was followed by US from 16-week gestation for cystic placenta. Beta HCG levels were normal. Normal karyotype 46,XX was found by amniocentesis. A female newborn was born at 36 weeks gestation. A partially cystic singleton placenta was submitted for pathological examination.
M&M: histological examination, p57 immunohistochemistry, CISH for ploidy, short tandem repeat (STR) analysis.
Results: a singleton placenta comprised of 2/3 normal placenta and 1/3 complete hydatidiform mole (CHM), largely degenerated, was diagnosed by histological examination and corroborated by negative p57 immunostaining in stromal cells of the molar villi. CISH revealed diploidy in the normal part and amnion and tetraploidy in the molar part. Sixteen microsatellites were studied by STR analysis, 12 of which were informative. The analysis revealed bipaternal molar tissue of dispermic origin. The paternal monospermic contribution to the normal part was different from that in the molar part, thus resulting in tripaternal contribution to the conceptus.
Discussion: gametogenesis, fertilization and early embryonic development are remarkably imprecise processes. A frequent chromosomal error is bipaternal triploidy. One of the major consequences is postzygotic diploidization, a process that may lead to the formation of CHM. Chimera is a single organism composed of two or more different populations of genetically distinct cells that originated from different zygotes involved in sexual reproduction (tetragametic). The possible mechanisms leading to the formation of chimeric placenta in our case are discussed.