Multiclefted nuclei. A helpful feature for identification of intermediate trophoblastic cells in uterine curetting specimens.

Intermediate trophoblast is a distinct form of trophoblast, the presence of which in uterine curettings is considered a reliable indicator of intrauterine pregnancy even in the absence of chorionic villi. However, the appearance of intermediate trophoblastic cells have not been described in sufficiently specific terms to permit their reliable identification, and distinction from decidual cells can be difficult. We have noticed for some time that the intermediate trophoblastic cells often show multiple deep clefts in the nuclei, and the present study was performed to address the issue of whether this nuclear feature is reliable for their identification. We reviewed 242 uterine curettings of intrauterine pregnancy, documented by the presence of chorionic villi, and were able to find a distinct population of cells with large, hyperchromatic, multiclefted nuclei scattered in the decidua in 88% of the cases. In most instances, these cells produced a characteristic variegated pattern that was readily recognizable at low magnification. Positive immunostaining for cytokeratin (CAM 5.2) in these isolated cells within the decidua confirmed their trophoblastic nature. In contrast, multiclefted nuclei were absent in the 51 negative control cases, which included decidualized endocervical polyps (40 cases), uterine curettings from patients with tubal pregnancy (10 cases), and endometriosis with decidual change (one case). We conclude that intermediate trophoblastic cells can usually be reliably identified in curettings of intrauterine pregnancy by their characteristic nuclear multiclefting.