The internal vertebral venous plexus prevents compression of the dural sac during atlanto-axial rotation.
Deformation of the extradural space and the possibility of impression upon the dural sac during atlanto-axial rotation are investigated. Atlanto-axial rotation leads to a reduction in the cross-sectional area of the bony spinal canal of approximately 40%. Atlanto-axial rotation was recorded by endocanalar views from a video camera fixed inside the skull of six unembalmed cadavers. Axial thin-section T1-weighted MRI slice sets were acquired from three volunteers (mid-position and maximal left and right rotation of the head and cervical spine). The axial cross-sectional areas of the bony spinal canal, dural sac and spinal cord were measured. In two other persons post-gadolinium contrast-enhanced T1-weighted MRI volume scans with fat-suppression prepulse were acquired (mid-position and rotation) to determine venous contents of the extradural space. The 50:50 ratio between left and right extradural halves in mid-position changed to an ipsilateral:contralateral ratio of 20:80 in maximum rotation at the level just above the lateral C1-C2 joints. Directly below these joints the opposite occurred. The post-contrast studies showed an enhancing internal vertebral venous plexus (IVVP), which almost completely occupied the extradural space at the atlanto-axial level. This could not be shown in the cadaver experiments, because of absence of blood and cerebrospinal fluid (CSF) pressure. During atlanto-axial rotation blood displacement in the IVVP allows major deformations of the extradural space. This prevents dural sac impression.
Reesink
E M
EM
Department of Anatomy/Embryology, Maastricht University, The Netherlands.
Wilmink
J T
JT
Kingma
H
H
Lataster
L M
LM
van Mameren
H
H
D000368:Aged; D000369:Aged, 80 and over; D001268:Atlanto-Axial Joint / Q000033:anatomy & histology* / Q000502:physiology*; D002102:Cadaver; D004388:Dura Mater; D006801:Humans; D008279:Magnetic Resonance Imaging; D008875:Middle Aged; D012399:Rotation; D013116:Spinal Cord / Q000033:anatomy & histology* / Q000502:physiology*; D013117:Spinal Cord Compression; D014680:Veins