Figure 1. Microscopic demonstration of physiologic transformation of myometrial segement of the spiral artery in normal pregnancy at term.
Placental bed biopsy specimen was immunostained for cytokeratin-7 to locate trophoblasts (arrowheads) infiltrating the arterial wall, and additional Periodic Acid Schiff (PAS) staining was performed to identify fibrinoid (arrows). Spiral arterial lumen is dilated, and fibrinoid replaces the media and intima. L: spiral arterial lumen (Cytokeratin 7-PAS staining, X100).