Prevalence and significance of implantation site trophoblastic atypia in hydatidiform moles and spontaneous abortions.

The authors studied the prevalence and significance of implantation site trophoblastic atypia in hydatidiform moles and spontaneous abortions. Three pathologists independently categorized 99 early abortion specimens regarding diagnosis (spontaneous abortion, partial hydatidiform mole, complete hydatidiform mole); qualitative atypia of implantation site trophoblast (absent, mild, moderate-severe); and quantitative atypia of implantation site trophoblast (absent, focal, diffuse). Interobserver agreement was good to excellent regarding diagnosis (kappa 0.66-0.79) and poor to fair regarding qualitative atypia of implantation site trophoblast (kappa 0.20-0.43). By consensus diagnosis, implantation site trophoblastic atypia was mild and focal in 5% of 22 spontaneous abortions; predominantly focal in 40% of 30 partial moles (33% mild atypia; 7% moderate-severe atypia); and, predominantly diffuse in 87% of 47 complete moles (21% mild atypia; 66% moderate-severe atypia). Among hydatidiform moles, the subsequent development of persistent gestational trophoblastic tumor did not relate to the degree of implantation site trophoblastic atypia. The authors conclude that trophoblast of the implantation site exhibits focal, mild atypia in some partial hydatidiform moles,and diffuse marked atypia in most complete hydatidiform moles. Thus, implantation site trophoblastic atypia may be a useful pathologic guideline regarding the diagnosis and classification of hydatidiform moles.