Arteries and veins of the lumbar nerve roots and cauda equina.

An abundant vascular system supplies the nerve roots, within the cauda equina, in the spinal canal and in the nerve root tunnels. The arterial supply of nervous tissue, as noted by previous observers, is "just adequate for its minimal needs." The veins of the area are classified into 3 groups, those of the spinal canal within the extradural space, those of the nerve roots themselves (radicular veins) and those which drain the bony skeleton. These thin-walled venous channels are a source of serious bleeding both at operation and in the postoperative period. Elsewhere in this symposium, emphasis has been placed on the way in which spinal stenosis and pressure on nerves cause the complex group of symptoms. Pressure on arteries, veins and capillaries can impair nerve conduction, with changes in sensation and loss of motor power in one or both limbs. If the pressure is prolonged, irreversible changes take place in the substance of the nerve roots. Recovery of sensation and of motor power following adequate surgical decompression will then be incomplete.