Contrast enhancement in lumbar spinal nerve
roots has been seen variably in patients with
spinal stenosis, herniated disks, or previous
laminectomy (1–5). It is thought by some investigators
to signify radiculopathy and a disruption
of the normal blood-nerve endothelial barrier
(6). The enhancement in spinal nerve roots
secondary to nerve root compression typically
extends from the point of compression to the
cauda equina, probably because the extravasated
contrast medium diffusing proximally
through the nerve root meets a barrier at the
Obersteiner-Redlich zone, the sharply defined
and irregular transition region between nerve
roots and spinal cord (6). The enhancement
secondary to an injury of the nerve root is more
intense than the faint generalized enhancement
of nerve roots seen in about 50% of persons (6);
this enhancement is more conspicuous with a
dose of 0.3 mmol/kg than with a dose of 0.1
mmol/kg (7). Whether the enhancement occurs
because of a fibrotic reaction to the compression
of the arachnoid, as one investigator speculated
(7), or represents demyelination, edema,
or inflammation in the nerve root, as has been
found histopathologically in some cases of
nerve root compression, is uncertain. Therefore
we studied histopathologically nerve roots demonstrating
contrast enhancement produced experimentally
by chronic compression.