SOFT-TISSUE ANATOMY WITHIN THE VERTEBRAL CANAL IN PREGNANT-WOMEN

To clarify pregnancy-induced changes in soft tissue anatomy within the vertebral canal, we have studied magnetic resonance (MR) images of th e lumbar spine in three women. In each subject, T2-weighted axial MR i mages were obtained both before pregnancy and at 32 weeks' gestation, and the paired images were compared. The extradural venous plexus was engorged significantly in supine parturients. In addition, the engorge d extradural venous plexus displaced the dura away from the wall of th e vertebral canal in a posterior direction, which resulted in a decrea se in the volume of the cerebrospinal fluid in the dural sac. These fi ndings confirmed the long-held concept that the engorged extradural ve nous plexus in supine parturients decreases the effective capacity of the extradural and subarachnoid spaces.