A well-described cause of CES is spinal stenosis with canal
narrowing and ligamentum flavum infolding. Histologic
examination of compressed nerve roots reveals congestion
and dilation of intraradicular veins with infiltration of
inflammatory cells. Magnetic resonance imaging (MRI)
has been used to confirm edema of the cauda equina at the
stenosed segments.3,21,22
Serotonin may have an advanced role in the nerve root
compression cycle.23 Normally, serotonin has a vasodilative
effect on healthy nerve roots. Chronically compressed
nerve roots react with vasoconstriction in the presence of
serotonin. In a study of 45 dogs, Sekiguchi and colleagues23
inserted balloons deep to the lamina and kept them inflated
for 1 week; their results suggested that endothelial cell
dysfunction induced by serotonin might lead to contraction
of blood vessels under chronic compression.
In a 2004 follow-up study with rats, Sekiguchi and colleagues21
found that mild cauda equina compression induced
tumor necrosis factor a (TNF-a) expression and demyelination,
though increased compression induced TNF-a expression
and degeneration associated with macrophage invasion.
They also discovered that lesions proximal to the dorsal root
ganglion may not produce significant allodynia.