Light- and electron-microscopic study of the near-term paraplacenta of the domestic cat. II. Paraplacental hematoma.

: In the near-term paraplacental extravasate zone of the domestic cat, which includes paraplacental junctional areas and marginal hematomas, the uterine epithelium becomes highly proliferative, especially on the folds or protrusions, This hyperplastic surface and the adjacent connective tissue become symplasmic, degenerate and eroded, eventually resulting in maternal vascular breakdown. The uterine lumen thus contains maternal blood in addition to sloughed uterine cells. The adjacent cytotrophoblast apparently phagocytoses and ingests this material. Various stages of phagolysosomes containing erythrocytes of variable density are seen in these cells, as are myelin-like structures, ferritin, glucogen and lipid droplets. Crystalloid iron deposits are seen in the basal lamina and connective tissue subjacent to the hemophagous cytotrophoblast.