The internal vertebral venous plexus prevents compression of the dural sac during atlanto-axial rotation

Abstract

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.

The vertebral venous plexuses: The internal veins are muscular and external veins have valves

“…providing structural support to prevent overdistension or collapse, and regulating the direction and velocity of venous blood flow. However, this extraordinary venous architecture may also be linked to other potential functions of the IVVP including: acting as an extradural buffer to prevent compression of the dural sac with spinal movements (Reesink etal.,2001); assisting the regulation of intracranial pressure (Herlihy,1947); assisting with the reabsorption of cerebrospinal fluid (Zenker etal.,1994); and thermoregulation of the central nervous system (Zenker and Kubik,1996). This latter suggestion is particularly intriguing in view of the association we frequently observed on histology between small arteries and veins within the IVVP.…”

Das zerebrospinale venöse System

“…Diese Eigenschaft ist vermutlich durch den höheren CSF-Druck zu erklären. Der Venenplexus übt hingegen eine Pufferfunktion aus und kann durch schnelle asymmetrische Ströme die Raumänderung ausgleichen und der Kompression des Duraschlauchs entgegenwirken 26 .…”

Possible thermoregulatory functions of the internal vertebral venous plexus in man and various other mammals: Evidence from comparative anatomical studies

“…Several functions have been proposed for the IVVP. It plays a role as an alternative venous pathway also responsible for the spread of metastases and infections (Batson,1940; Wiley and Trueta,1959), in postural hemodynamics (Eckenhoff,1971; Blix et al,1975; Zippel et al,2001; San Millán Ruiz et al, 2002; Gisolf et al,2004) and in pressure‐volume regulation of the cerebrospinal fluid (CSF) (Reesink et al,2001). These last authors described that in humans the movement related volume‐changes of the upper cervical vertebral canal are compensated for by filling or emptying of the IVVP in that region, thereby allowing enough space for the spinal cord at these levels.…”