Do vertebral veins have valves?

Matthew Restieaux was recently awarded a "highly commended" award for his summer research project "Do vertebral veins have valves?".

Matthew worked with Professor Mark Stringer in the Department of Anatomy.

Venous blood drains from the vertebral column via an extensive network of veins, the vertebral venous plexus (VVP).

This plexus extends the entire length of the vertebral column and is made up of veins outside (external) and inside (internal) the vertebral column.

Authoritative anatomy texts state that these veins have no internal valves, allowing blood flow in both directions and facilitating the spread of malignant tumours that invade blood vessels.

The aim of this study was to identify whether vertebral veins are in fact valveless.

Segments of VVP were removed from 11 adult cadavers (6 female, mean age 79 years, age range 64-97 years) and examined for the presence of valves using a dissecting microscope.

Twenty-six valves were identified in 56 segments of external VVP veins.

Most of these valves had two cusps.

The cusps were orientated such that blood flow was directed from the external VVP towards the internal VVP.

The internal VVP consisted of four longitudinal veins (two anterior and two posterior) surrounding the outer membrane of the spinal cord.

The longitudinal veins were connected by transverse veins in a ladder-like arrangement.

No valves were found in the internal VVP but these veins had striking internal bridges and folds (trabeculations) not previously described in the anatomical literature.

Microscopy confirmed the presence of extensive trabeculae within the internal VVP veins and showed that these trabeculae were made up of smooth muscle and collagen within which a few small muscular arteries were also visible.

These novel findings contradict standard anatomy teaching i.e. veins of the external vertebral venous plexus do possess valves.

Our findings also suggest that the veins of the internal VVP are not simply passive conduits for the flow of venous blood within the vertebral column.

Their trabeculations may act to (i) provide mechanical support protecting the veins from overdistension or collapse, (ii) regulate blood flow direction and velocity, or (iii) may possibly be involved in processes such as temperature regulation of the spinal cord.