PURPOSE: To examine histopathologically the endothelium of contrast-enhancing spinal nerve
roots. METHODS: In five adult baboons, chronic compression of the left S-1 spinal nerve root
sufficient to produce a change in the evoked potential was produced by means of a suture tied
around the nerve. The animals were studied with MR at 8 and 16 days after nerve compression and
then killed for histopathologic and electron microscopic studies. Histopathologic changes in the
nerve roots demonstrating contrast enhancement were described. RESULTS: In all compressed
spinal nerves, contrast enhancement was observed. Histopathologically, wallerian degeneration of
the root and inflammation and disruption of the endothelium of capillaries in the spinal nerve were
evident. CONCLUSIONS: Degenerative changes in the nerve root and the capillary endothelium of
a lumbar spinal nerve are associated with contrast enhancement.