title: Differences in lumbar dural sac dimension in supine and lateral positions in late pregnancy: a magnetic resonance imaging study.
abstract: BACKGROUND
  This study was designed to quantitatively investigate differences in lumbar dural sac dimensions between the lateral and supine positions in late pregnancy.
  
  
  METHODS
  Ten healthy volunteers with singleton pregnancies at 28-39weeks of gestation were included. Magnetic resonance imaging was performed in random order while subjects were in the left lateral and supine positions. Lumbosacral axial scans were obtained at the L1-2, L2-3, L3-4, L4-5 and L5-S1 intervertebral disc levels. The axial section area, anteroposterior maximum diameter and transversal maximum diameter of the dural sac were measured and differences between these parameters in the lateral and supine positions were compared.
  
  
  RESULTS
  The axial section areas of the dural sac at L1-2 (P<0.001), L2-3 (P=0.001), L3-4 (P<0.001) and L4-5 (P=0.005) and the transversal maximum diameter of the dural sac at L1-2 (P<0.001), L2-3 (P<0.001), L3-4 (P<0.001) and L4-5 (P=0.001) were greater in the lateral position compared with the supine position. The anteroposterior maximum diameter of the dural sac at L4-5 was greater in the lateral position compared with the supine position (P=0.019) but there were no significant differences at other levels. The magnitude of the differences in axial section area and transverse maximal diameter were similar among the levels studied.
  
  
  CONCLUSIONS
  The axial section area and the transversal maximum diameter of the dural sac in the lumbar area are reduced in the supine compared with the lateral position in late pregnancy.
authors.affiliation: Department of Anesthesiology, Peking University Third Hospital, Beijing, China.
authors.forename: Fei
authors.initials: F
authors.lastname: Xu
authors.affiliation: Department of Radiology, Peking University Third Hospital, Beijing, China.
authors.forename: Ying
authors.initials: Y
authors.lastname: Liu
authors.affiliation: Department of Obstetrics and Gynecology, Peking University Third Hospital, Beijing, China.
authors.forename: Yuan
authors.initials: Y
authors.lastname: Wei
authors.affiliation: Department of Obstetrics and Gynecology, Peking University Third Hospital, Beijing, China.
authors.forename: Yangyu
authors.initials: Y
authors.lastname: Zhao
authors.affiliation: Department of Radiology, Peking University Third Hospital, Beijing, China.
authors.forename: Huishu
authors.initials: H
authors.lastname: Yuan
authors.affiliation: Department of Anesthesiology, Peking University Third Hospital, Beijing, China. Electronic address: xiangyangguoby@163.com.
authors.forename: Xiangyang
authors.initials: X
authors.lastname: Guo
mesh_terms: D000328:Adult; D002555:Cerebrospinal Fluid / Q000502:physiology; D005260:Female; D006801:Humans; D007403:Intervertebral Disc / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D008159:Lumbar Vertebrae / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D008279:Magnetic Resonance Imaging / Q000379:methods*; D011247:Pregnancy; D016683:Supine Position
keywords: Epidural venous plexus; Magnetic resonance imaging; Obstetric; Positional change