Figure 1.

Trophoblast inclusions (TIs) and calcified TIs (hematoxylin and eosin). Representative progression of TIs and calcified TIs identified in the chorionic villi examined for this study. (A) Single TI with central syncytial trophoblast nuclei (arrow) and circumferential cytotrophoblast (arrow head). Villus core (V) and intervillus space (I). (B) Multiple TIs in same field, some with clearly defined syncytiotrophoblast centers (long arrows) and surrounding cytotrophoblasts (arrow heads) and others with poorly formed centers (short arrows), possibly due to tangential sectioning of the TIs. (C) A TI with dense syncytial trophoblast core (arrow) surrounded by multiple cytotrophoblasts (arrow heads). (D) Very dense TI (arrow) with only a remnant of cytotrophoblast (arrow head). This is the step just before a TI becoming calcified. Fetal vessel containing erythrocytes (R). (E) Central syncytiotrophoblast core has become so dense that only a few nuclear profiles are recognizable (arrow), whereas the surrounding cytotrophoblasts have matured and have begun to fuse and form another layer of syncytiotrophoblasts (arrow heads). Intervillus space (I). (F) A TI with obvious lines of calcification but a central core with syncytiotrophoblast nuclei can still be identified (arrow). Cytotrophoblast remnant (arrow head). Fetal vessel containing erythrocytes (R). (G) A TI with mostly calcified core (arrow), with a few residual syncytiotrophoblast nuclei (arrow head). (H) Almost completely calcified TI with loss of calcified material likely secondary to histologic sectioning (arrow) but still with a few visible syncytiotrophoblast nuclei (arrow heads). Tangential section through a more recently formed TI (*).