Confirming the presence of an intrauterine implantation site in endometrial curettings without recognizable chorionic villi is important in the diagnosis and management of ectopic pregnancy. In order to evaluate histologic features that might be useful in establishing the diagnosis of an intrauterine gestation, we conducted a retrospective review of 150 endometrial curettings obtained from women with incomplete abortions or ectopic pregnancies. The specimens were divided into three groups: 1) intrauterine gestations with villi, 2) intrauterine gestations without villi, and 3) known ectopic pregnancies. Differences in the histologic appearance of the endometrium between intrauterine and extrauterine pregnancies were evaluated, with emphasis on 34 curettings from intrauterine gestations in which no chorionic villi were identified and 12 curettings from ectopic gestations. Histologic features assessed in these 46 cases included the presence of intermediate trophoblastic cells; caliber, thickness, and hyalinization of spiral arteries; the presence of a fibrinoid matrix; the Arias-Stella phenomenon; decidua; inflammation; and thrombosis. Intermediate trophoblast in vessels and/or decidua was recognized by conventional light microscopy in 14 (41.2%) of 34 intrauterine cases with no villi, but was identified by immunoperoxidase reactions for hPL in 24 (70.6%) and keratin in 20 (58.8%) of these cases. Endometria from intrauterine gestations also demonstrated a significant increase in arterial wall thickness, hyalinization and lumen diameter, and thrombosis when compared with the endometria associated with ectopic pregnancies. Intermediate trophoblast, enlarged hyalinized spiral arteries, and fibrinoid matrix were not seen in any of the ectopic pregnancies. Based on these findings, intrauterine implantation can be diagnosed, in the absence of villi, by the presence of intermediate trophoblast associated with enlarged vessels replaced by hyaline, or with fragments of fibrinoid matrix.
© 1988 The American College of Obstetricians and Gynecologists