Blood supply of spinal nerve roots. An experimental study in the rat.

The blood supply of rat spinal nerve roots was investigated using a variety of methods, including preparation of vascular casts with Microfil, alkaline phosphatase histochemistry and Epon embedding for light and electron microscopy. Dorsal and ventral roots were sampled and portions from the spinal cord, dorsal root ganglia and peripheral nerve were taken for comparison. There were two different types of vessels in the roots; the large extrinsic (radicular) and the minute intrinsic vessels of the nerve root parenchyma. The radicular vessels follow a straight course along the longitudinal axis of both ventral and dorsal roots. Their diameter appears to vary in different topographical regions. They are united with the longitudinal spinal cord arteries and are a major source of arterial supply to the spinal cord. There are also many small communicants with the intrinsic root vasculature. The radicular vessels are located in the root sheath and are surrounded by cells and collagen fibers forming this sheath. The intrinsic vessels of the spinal roots form a plexus of minute vessels, chiefly capillaries. Most of them are longitudinally arranged along the roots but there are also many loops and twisted portions. There are many direct connections to neighbouring vascular networks. The microvessels are surrounded by a basement lamina and wide, collagen containing extracellular spaces. The intrinsic vascularization of the roots is similar to that in the endoneurium of peripheral nerves, i.e., chiefly a plexus of minute vessels. Many direct communicants exist between these intrinsic vessels and blood vessels in the spinal cord parenchyma, ganglia and nerve.