Fig. 4. Computerized coronal magnetic resonance images of the spinal canal between T12 and S1 in the pregnant and nonpregnant states. Multiple coronal images are computer-processed into one image in alignment with the curvature of the ventral epidural space. Those images show the curved surface with the ventral epidural space. The engorged epidural venous plexus in the ventral epidural space was observed between Th12 and S1 in the pregnant state, but not in the nonpregnant state. In the pregnant state, arrows indicate the engorged plexus in the ventral epidural space ( white arrows = longitudinal veins; dotted arrows = crossed veins). The situation of the engorged epidural venous plexus resembles a ladder.